I'm not sure I'm following the problem. If I bring my firearm in for repair. Before a hand it over I clear it. Then the nice man behind the counter, clears it. If anyone hands me a gun, I clear it. Are you saying that you recieved firearms in your shop that no one including your employees bothers to clear? Maybe I'm just not understanding.
That's not the issue, it's inconsiderate and dangerous.
What if the customer brings in a loaded firearm, round in the pipe, safety off, and he manages to let one fly? Hard telling how many gunsmiths have been shot because their customer brought in a loaded gun that "didn't work" but was "clear" and before the smith could verify for himself it was unloaded, he became the victim of someone's stupidity.
I've had more "unloaded" guns pointed at my head, heart, and nuts than I care to think about.
If you have a firearm or muzzle loader that's loaded and absolutely will not function and you can't even eject the live round out, it's one thing. It's also a courtesy to inform the person who's going to be working on your gun that there is a live one in the chamber.
But if the owner is too lazy or inconsiderate to clear their gun before handing it over to someone for work, there needs to be some repercussion to their actions