A lot of people who come back "Denied" don't know beforehand that it's going to happen (the system has lots of bad records in it, very few people actually know their full legal status), and they certainly don't charge people with felonies when it happens.
I'd imagine people would be quite well aware whether they've ever been convicted of something or aren't eligible to buy a gun.
You'd be surprised. Cock-ups with the national instant background check service happen all the time. You have to remember that a lot of the information it's getting is coming from hand-keyed records of old cases, from all 50 states, each of which uses (or used) a different format on its documents. Someone enters the wrong code when entering an old case record, and boom, what was a misdemeanor now looks like a disqualifying felony in the system. Or a notification of completion of the terms of probation gets lost in the mail, and boom, someone is stuck indefinitely in the system as ineligible to buy a firearm even if the original charge was expunged a decade ago.
Unless you've never so much as gotten a traffic ticket in your life, you are in a court system for something somewhere, and the potential for mistakes is ever-present. Have you really not heard
dozens of horror stories about personal government records getting messed up? I sure have!
Returning from my digression, I'm looking forward to the photos of the wares for sale.