During my college years (and about a year after graduating), I worked at an AutoZone that was the largest store in it's district. For 3 years, I was an assistant manager there. I went into that job as a well-mannered guy with a positive outlook on life, and I left as a cynical guy with nothing but spite and hatred for his fellow man. Slinging auto parts will do that to you. And yes, I have stories.
How about the time when a guy was waiting to check out and a customer cut him in line, and as a result, the box of brake pads the customer had in his hand was launched at my head for ringing him up? The store was packed from front to back on a busy Sunday afternoon, and there were only two of us working thanks to a fellow employee not showing up that day. I didn't have time to explain to people the etiquette of how to stand in line. Luckily I dodged the brake pads.
Then there are the countless idiots that go through the same part 20+ times not realizing that the part they are replacing is not the culprit. The customer usually comes in and slams the part on the counter, swearing about the crap quality of their parts, and demanding another one. After a while, my manager would catch on to some of these people and turn them away. That was always the best, because all hell would brake loose, and the rest of us would sit back and watch.
The concept of "Universal Fit" doesn't compute with some people, which was annoying. One time, we had a bunch of stupid garbage accessories, like pedal covers and underbody neons, on a clearance table. It was clearly marked ALL SALES FINAL. This guy with a red early 2000's 4 door automatic Ford Focus with the big useless wing, giant dragon decals on the sides, and chrome hubcaps asks me if the neons fit his car. You all know what kind of dirt bag I'm talking about. I explain that they are universal fit. He didn't get it, telling me that I didn't answer his question. So I told him that they will fit any car, because they are universal, and that's what that word means. I also clearly explained that it was an ALL SALES FINAL deal, even though the purple neons were still over $100 on clearance. So he buys them. You all know where I'm going with this.
Not 2 hours later does this genius come back, saying that I lied to him by telling him that they would fit, demanding his money back. My manager sent him packing by his ultimate tactic of telling him no at least 3 times and ignoring the customer until the store closed if he stuck around that long.
Some of the more interesting dealings I had were with non-English speaking customers. Please note that I am not trying to be offensive in any way (my dad is an Italian immigrant that had to learn English when he got here), but the language barrier that existed would cause issues, and there was no way of getting around it.
We had a regular contingent of Brazilian immigrants that would come into the store. Most of them were nice guys, but getting the parts they needed could be difficult. For some reason, they would always bring in parts that are actually parts of parts, like little pieces of an oil pump assembly, and they would want just that part, which nobody sold. I had no clue how the hell they could even disassemble some of these parts that much to know that these little pieces would even be the problem. Truly amazing.
The hardest one was one time one of the regulars came in and we played a game of charades for about a half hour with this round metal disc with rectangular bars attached to the disc. First, I thought it was a flywheel. Then, perhaps some sort of weird pulley? Nope, it was half of a vented brake rotor.
I have many more stories of being in the trenches of the Auto Parts Sales business.