Here ya go. Good luck finding any reference to bans on microphone or harmonica returns.
New Jersey (ZZounds is based in NJ) Dept of Health Statutes.
The only reference I can find to a microphone is in the definition of what a hearing aid is in the state of NJ.
I managed a music store for 6 years myself and I can say we used that same line to keep dopes from buying mics on Friday and returning them after the gig on Monday. Harmonicas we simply didn't take back because that is friggin gross.
I have never seen a health dept inspector go to any bar, bingo hall, church, stadium, concert venue, pawn shop, bus terminal, subway station, radio station, TV station, recording studio, or any where else microphones are in public use and ask to see their mics. It doesn't happen. The "can't return for health reasons" is a load of crap.... because everyone uses a Schoeps omni as a vocal mic in a punk band.

And if a dude did stop by your store, I can gurantee he was bored or was checking on something unrelated to microphones... like the sewage lines to the back room toilet. We sold used flutes, clarinets, saxophones, trumpets, trombones, tubas, susaphones, oboes, bassons, ad nauseum and people were actully blowing spit and snot into them. No health dept concern there.