Yup, NEVER talk to a cop (unless you happen to have to report a crime for insurance purposes, or can offer direct immediate aid for something like a lost child).
In many cases these guys are just looking for something to do - 'occupational therapy'. It's probably worse in lower-crime suburban areas, as those activity reports need to fill up...
This text linked/quoted below here, while ever-so-slightly off-topic, relates to what to do if the BATF comes to your gunshop. Nevertheless it contains many pearls of wisdom for dealing with LEOs and search warrants in general - regardless of any firearms issues - and also deals w/division of labor and rights of entry/inspection matters of accompanying gov't employees who aren't sworn LEOs. I've attached the section called "The Raid" which is near the end of the article as it has lotsa info pertaining to general search warrant issues.
This article was written by Jim Jeffries, a former Fed lawyer and gunrights attorney who deals with lots of BATF issues.
Fortunately technology is going to be very helpful in the future. Low-cost home surveillance cameras can surreptitiously record many hours of encrypted, near-HD-quality video and quality audio in multiple areas in & around your home. Not only that, you can goad the LEOs into illegally seizing (stealing) what they think is the only copy of the information, while other cameras distribute the video of this theft to the internet
I believe this is how some Oakland CA cops got burned investigating a Ms Field's robbery - they helped themselves to sodas & food (unpaid).
from
http://www.gunowners.com/batf.htm:
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WHEN THE BATF COMES A-CALLIN'
by James H. Jeffries, III
"There is no wholly satisfactory substitute for brains, but silence does pretty well." --Anonymous
Probably one of the least favorite events for any Federal Firearms Licensee (hereafter "FFL") is a visit from the Bureau of Alcohol, Tobacco and Firearms (hereafter "BATF"). This can occur in one of at least six very different ways and your legal rights and recommended responses vary accordingly.
For purposes of the following discussion I will assume that you are a law-abiding licensed dealer or collector who tries to comply honestly with the federal firearms laws. If some of the discussion below seems excessively cautious, or even hostile to BATF, it is based on real world experience with an agency which has been found by Congress, by various federal judges and juries, by other federal and local law enforcement agencies, and even by some Presidents to be inept, indifferent to citizens' rights, and capable of the most outrageous abuses of the law.
BATF operates under the rationale of requiring you to comply with the law. I operate under the rationale of requiring BATF to comply with the law. I required this of BATF as a federal prosecutor for almost 30 years, and I require it as a private citizen and as a lawyer. You should require it as an FFL.
A non-licensee has no legal duty whatsoever to talk to or otherwise cooperate with a BATF agent (or any other governmental official). It is a sad commentary on our times and the state of our federal government (and especially BATF) that the appropriate legal advice from a defense lawyer to a non-licensee confronted by a federal or state law enforcement officer can be capsulized in a single sentence called RULE ONE: Silence is golden; or what part of "no" don't you understand? If you are an FFL, however, additional considerations come into play.
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{big snip}
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When faced with the prospect of providing information to the government, keep in mind that there are only two legal options: silence or complete truthfulness. Lying (even by partial truths or literal but misleading true answers) is never an option. A false statement to a federal officer in his official capacity is a felony akin to perjury, and usually much easier to prosecute and prove than the matter being investigated. If you cannot speak truthfully without incriminating yourself or injuring your legal interests, then remember RULE ONE.
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{snip}
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Occasionally a tracing inquiry will be made in person by one or more special agents. They are, of course, purely criminal investigators whose only function (and interest) is to put people (including firearms dealers) in jail. Write down the names and badge numbers of all present. If anyone present is not a BATF special agent, inquire why that person is present (and later note the response in writing). If there is more than one agent, inquire why. If anyone refuses to display official identification direct them to immediately leave the premises. If they refuse, call the local sheriff or police and make a trespassing complaint.
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{snip}
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Remember, refusing to talk to federal criminal investigators and seeking legal counsel are not admissions of guilt or signs of a guilty conscience. They are manifestations that you are an American citizen aware of your legal rights and an individual who will not be bullied, coerced or frightened into giving up those rights. The agents already believe you are guilty; their job is to prove it. Your job is to avoid helping them prove it.
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{snip}
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Some of my bolder clients, who are truly tired of being harassed this way [[
undercover illegal solicitation]], are fully prepared to make a citizen's arrest in such circumstances and then call the local sheriff to come collect the offender (attempts and solicitations to commit an offense are also crimes under federal and state law). If this appeals to you, make sure first that the law of your state permits a citizen's arrest. Know the amount of legal force you can use to effect such an arrest. Then cuff the son of a bitch and give him a taste of what he's probably trying to do to you.
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{snip}
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When a BATF inspector shows up for a compliance inspection, require credentials to be displayed by everyone present and note the full name of the inspector(s) in writing. Never permit a special agent or a state or local or non-BATF federal official to participate in a compliance inspection. These individuals have no authority under the inspection laws, and are there for some different (and more ominous) reason. A state official might have independent state-law authority to conduct an inspection or investigation, but he has no right to do it in tandem with a BATF compliance inspection. You should require other inspectors or investigators to get in line so that you can deal with them at a separate time. If they refuse to leave, call the sheriff and swear out a trespassing complaint. If a BATF special agent, a firearms specialist from BATF's Technology Branch in Washington (part of the criminal enforcement branch), or other criminal law enforcement type is present, this is not an ordinary compliance inspection and you should immediately terminate it, direct the individuals to leave and contact legal counsel.
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The simple truth is that you never want a BATF employee in your home if it can be avoided.
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The Raid
This is an event which means you are in deep, serious. It is the execution of a judicially-issued search and seizure warrant (and occasionally also an arrest warrant) by BATF special agents, frequently accompanied by agents of other federal or local agencies, on premises owned, occupied or inhabited by you.
When a raid team shows up at your premises and announces (usually by breaking down your door, sometimes by killing your dogs and throwing flash bang grenades at your women and children) that they have a federal search warrant, you must instantly do several things. You must first of all mentally assimilate the fact that they are law officers rather than a rampaging motorcycle gang (which they often resemble in both appearance and behavior). Having identified them as law rather than outlaw, you must freeze in place in a non-threatening posture and attempt to stabilize the situation until some of their law-enforcement adrenalin (the most dangerous drug on the street) has bled off. If only a search warrant is involved, you must then recover your wits sufficiently to do the following:
(A) Try to note and record the identities of as many participants as possible, by name, agency, badge number, and physical description.
(B) Ask for a copy of the warrant.
(C) Disable -- not unplug, disable -- your telephones and fax machines.
(D) Gather your family, children and pets and leave the premises.
(E) Call your lawyer.
You may be prevented from doing some or all of the above things by legally illiterate agents, but that will simply lay the foundation for your own day in court.
A federal search warrant authorizes only the search of a specified premises and only the seizure of specifically described items. Corollary to the execution of a warrant, the law permits the agents to make a forcible entry if that becomes necessary after knocking and announcing their identity and purpose, to control the premises, and to take reasonable precautions for their own safety -- such as a pat down for weapons of those persons present and assigning an agent to watch over and accompany anyone moving about on the premises. The law authorizes the agents to prevent the destruction of evidence or contraband and it protects them against being assaulted or interfered with. It is a serious federal crime to assault a federal officer or to obstruct execution of the warrant. Don't turn a possible later indictment into a sure one. Never assist the raiding party in locating the items described in the warrant. They have the right to search, but not the right to find. Do not open locked compartments, safes or rooms for them or provide them with keys or combinations. Do not talk to the raiding officers other than to request identification and a copy of the warrant. Resist the compulsion to show what a good guy you are; these are not your friends and they are not there to help you.
A search warrant does not authorize agents to arrest you or anyone else on the premises (although assaulting the agents or forcibly interfering with the execution of the warrant will justify a warrantless arrest) and it does not authorize them to handcuff you, restrict you to a particular place or prevent you from leaving.
You have a perfect right to leave the premises and should do so immediately. If you are physically prevented from leaving, you have just been falsely arrested in violation of the Fourth Amendment and will have your recovery later in court as well as taking some of the other retaliatory measures promised above. You must get yourself and your family out of the house for several reasons:
(A) to avoid the personal insult, humiliation, provocation and indignities which many agents seem to enjoy;
(B) to avoid a potential life-threatening situation; and
(C) to avoid creating evidence against yourself (RULE ONE). There is no useful purpose your remaining on the premises can serve; if the agents are going to plant evidence or destroy property, they will do it whether or not you are present.
You will need as much information about identities, badge numbers and descriptions as you can manage in the minutes before you leave. These will be useful later when you assert or defend your rights. But they are not a reason to delay leaving the premises promptly. You are legally entitled to a copy of the warrant, but do not remain on the premises if you are refused.
You should disable your telephones and fax machines before leaving in order to prevent the agents from illegally seizing evidence (calls and faxes) which might come in while they are on the premises. Such items did not exist when the warrant was signed and cannot possibly be covered by the warrant. Their seizure will probably therefore be illegal; but it is better to prevent such seizures from even happening. If you are physically prevented from disabling your own property, go somewhere else and place incoming calls to all your lines and keep the circuits open.
Now, call your lawyer.
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The author is a retired U.S. Department of Justice lawyer and a retired colonel in the Marine Corps Reserve practicing firearms law in Greensboro, NC. He is a 1959 graduate of the University of Kentucky and a 1962 graduate of the UK College of Law, where he was Note Editor of the Kentucky Law Journal. 
