Our town is small enough that we'd know them all anyway. If they sent a detective or a uniformed cop in plainclothes we would know at all the places I might have a drink. If they took a person in some trouble and sent them in as an informer we'd know that too.

I guess it helps to hang out in "Cheers" type bars where everyone knows each other and the Owners and staff actually get along with the police.

Edit: That works both ways... I have a friend with a business downtown. He got popped for DUI 2nd a month or so ago, along with a DUS. (Yeah, not too smart but he's gay so what do you expect- he's tortured). Anyway, I hear he is riding dirty again to get to his business and it's only a matter of time until the city cops start nailing him unless he buys a new car they don't know.