Don't waste your time with UPS Stores, as previously mentioned they are franchises and apparently can set their own rules. I ran into a similar issue with my local UPS Store a few years ago and it wasn't even a firearm related item. Received the wrong part for my truck I had ordered, the place I ordered it from sent me a prepaid return packing slip for UPS so I was dumb enough to go to my local UPS Store. The young kid behind the counter placed my item on a counter behind him without attaching the label I came in with (I needed a box to return the item so I had already paid for the box but because a line had formed behind me the kid decided to speed up the process by throwing the stuff on the counter behind him apparently with the plan to box everything up after the line had been cleared out). Of course, I wasn't about to walk out the store with my return item laying on a counter, un-boxed and without my return label attached so I informed him I wasn't moving from the counter until I watched him package the item and attach the label.
TL;DR We went back and forth for about 3 minutes and when I pointed out that he could have just boxed the item and attached the label in less than a minute and instead arguing with me for 3 minutes thus holding up the line, he basically told me to "go F myself." So informed him to hand me back my item and refund me back my $3 for the box I had paid for, which ended up taking another 5 minutes and of course this whole time the line just keeps getting bigger behind me.
After I walked out and got back in my truck, I called UPS Corporate to file a complaint against the franchisee and while sitting in the parking lot on hold with UPS CS, the PoPo roll up on me and surround my truck. Apparently some young female coworker that was hiding in the back room during this whole affair decided to call the police and tell them I was "becoming aggressive and threatening towards staff and they feared for their lives..."
Of course I was calm the whole time I was in the store and after I was able to sort things out with the cops, by pointing out that I was on-hold with corporate and they could go in and check the surveillance tapes to see why my demeanor had been during the alleged "assault", they were good enough with that and after checking my ID and taking my name/license plate, they left me to complete my call with corporate, which BTW got me nowhere cause "UPS has no authority over their franchisee's."
Fun times.