Speaking to the original post, the answer is "Not unless..." and a few exemptions attach. The most important is 'exigent circumstances'; something happening NOW that cannot wait. I'm not sure about the background to the question, but any agency has to have probable cause, typically supported by a warrant in order to search a home or residence.
Under the Constitution and case law - legal decisions by courts - all searches must be 'reasonable'. All searches must be based on probably or reasonable cause. If the 'unannounced visit' is for the purpose of verifying the bound book against inventory, that's as far as it goes. (Does this get abused? Yes, it does and the courts are very quick to correct it when it happens. But that's another story.)
Also remember the 'plain sight' rule. If the BATFE examiner shows up to audit your books and inventory, don't leave the marijuana stash out on the counter. Just because his purpose is to check the guns doesn't mean he can't observe what is out in the open.