I have two, one about a customer and on about a store.
I was in my LFS just last weekend and a lady came in saying that her 2 Oscars had out grown her 1ft aquarium, she said they couldn't turn around properly anymore (they were 7"-8", I was quite amazed they grow so large and actually looked heathly). So Trev my LFS owner took the Oscars and started to show her appropriate fish for her tank like tetras and guppies.
Heres how the Conversation went down.
women "Ohh no, I wont more oscars, 4 this time".
Trev politly said "Oscars get to big for you tank, if you want more oscars you have to buy a new tank for them".
Woman "once they get to big I'll return them and get new ones".
Trev then said " I'm sorry but I wont sell you any Oscar it is inhumane to keep fish in conditions like that"
The woman replied with "the customer is always right and I want Osacrs"
Trev " I wont sell you those fish and no, the customer isn't always right, they are usually wrong"
Well the woman was not happy and started swearing "You F*%# Ass hole, I'll tell everyone that your store is crap and you treat the fish badly" and so on.
She then began to storm out the store when Trev said "ma'am, your Oscars" and she said "F*%#ing keep the fish I'll buy them else where"
On the way out she stop and said to me "Don't buy fish from here that guys a F*%$n ass hole" and I just said "Women, your F*%#n nuts" and she stormed off mumbeling(I was exspecting to get slapped).
Trevs wife came in and ask what was going on and he said "just some stupid F*%# *****", thats the only time I've heard him curse or even sound grumpy.
.............
Whilst on holiday during Nov/Dec at the GoldCoast I was in a Fish store just checking it out,

cons, dovii, umbree, jags, JD and texas

all illegal in SA.
A young couple and two kids were looking at fish when their kids spotted a RTC and wanted it (It was big, like 8" and thats why the kids liked it) and they decieded to buy a tank for it which measured 36"x14"x20"H (a biggish 3ft). The store guy told them it was actually bigger then your average RTC and would grow anymore, and they believe him not knowing any better.
So they guy went to get a bag, whilst he was gone I told them that the RTC got bigger then the tank, and they were like "no he told us that it was full grown". So I call a mate over that was there with me and ask "do RTC get bigger then 3ft?" and he said "Oh s**t yeah, why?". The couple said thanks and walk out the store.
The guy came back and I was standing looking at the RTC (looked really nice) and asked where they went, I said "You were telling them a load of crap so I told them the truth". The guy got angry to me to leave and never come back to the store, I said "fine, I live interstate and your a F*%#n wanker anyway".