When someone knocks on your door, even if they're in uniform, you do NOT have to open it.
If you don't open it, they can't "see" anything, they can't come in unless they have a warrant and while it may strain ones nerves to listen to the crap they'll shovel trying to get you to open your door, you are NOT OBLIGATED to do so.
You don't have to answer your phone just because it rings.
You don't have to accept certified mail just because someone paid to get your signature.
Sometimes you just have to say no.