Oh, where to start...
I once had a dealer refuse to give me back my pistol because he thought I was too young to own it (I was 19 or 20). A few years later I brought a pistol in to another shop to have night sights installed and when the clerk brought back my gun, he handed it to another customer because "obviously he is your father and it's his gun".
My favorite is when I was looking at a few different types of pistols at a rather large store. I was looking at the whole gambit - Glocks, HKs, XD, and 1911s, and honestly I was window shopping and trying to figure out what I liked but I wasn't going to buy anything that day (and told the guy I was working with that). Eventually we move to the 1911s and while extolling the virtues of the gun, he decided to pull a 1911 out from under the counter and start dry firing it at my chest!
Walked into one shop right after selling a motorcycle. I had more than $2,000 cash in my pocket and had my eyes on a DSA FAL. Couldn't get a single person behind the counter to agree to let me handle the rifle.
Yet another shop... was looking for an AK and was trying to decide between buying an AK pistol and SBRing it, or buying a 16" barreled Arsenal. Luckily the shop had both a SBR'd AK pistol and 16" AKs (though none in 7.62x39) so it was perfect to do a comparison. Anyway, I tell the guy behind the counter that I would like to compare both guns, and he doesn't say a word and just slowly walks away and starts chatting with a group of other guys working there. I wound up buying a 16" Arsenal, but not from them.
Bought a S&W Shield for my girlfriend (now wife) and because we were residents of different states, the transfer needed to go through a FFL in her state of residence. You wouldn't believe the number of FFLs who said "oh, we don't have universal background checks here (true), you can just give it to her" even after I explained why I wanted them to do the transfer. I finally wound up going to a small dealer and just saying "I'll give you $20 (their fee) to run this transfer" and they reluctantly agreed. I've never had so many people tell me to commit felonies in my life!
A lot of these events probably had to do with being in my 20's at the time. Some people in this industry apparently don't like the younger generation
Even years after these events occurred, I still refuse to visit some of these shops.
I don't have too many good gun shop stories, but I recently was buying a pistol as a gift for my brother in law and the store owner spent probably 20 minutes digging through the back of the store to find the right gun. Sure, they have inventory issues and it shouldn't take that long, but I really appreciated the effort. He also had the best price in town (and was actually comparable to online retailers).