Security, badges, information....
Doing security work & EP/protection details in everything from estates & gated communities to HUD/section 8 apt complexes & run down hotels, I can honestly tell you it's very easy for nearly anyone to get access to a home/property.
Many people think they can become PIs(investigators), bail agents/bounty hunters, repo-recovery agents, process servers, etc then go or do whatever they please. Wrong!
If a person knocks on your door & flashes any kind of badge or they are wearing "raid gear"(tactical vests, SAS holsters, hats, ski masks, etc), Id contact LE ASAP & let them deal with it.
Some repo agents & "bounty hunters" can be a bit extreme. They are not well regulated or supervised.
People see a badge or a ID then assume the person is a sworn LE officer.
In my state, security officers & PIs/PI interns have photo IDs. They are regulated by the Div of Licensing and can be cited or arrested for serious misconduct.
I dealt with a process server for a civil dispute in 2002. He was polite & professional with me. Most ethical process servers just go to a employer or contact the person then make arrangements to serve them thru a lawyer or other place.