Oh, I remember my days of working in customer service- people can be real doozies!!
I worked for a couple of years at a mid-priced ladies' store in the mall. There were these 2 nice older ladies, very well dressed and sweet, who would come in and purchase suits and dresses as soon as they came in to the store. They would pay full price. Well, about 5 months later, when we had our end of season clearance and all the leftover merchandise was marked down to its final price, they would come back in, suits and dresses STILL IN THE ORIGIONAL BAGS, WITH THE RECEIPTS ATTACHED, and demand a "price adjustment" of the rock-bottom, final clearance price. Since our store had the policy that each customer could get one price adjustment on any certain item, we would have to do it for them. We would try to tell them (each and every time they would pull this) that this was the last time we could do this for them, but they kept right on bringing back every single full price suit and dress they bought the entire 3 years I worked there. Those 2 ladies sure did get some GREAT deals off of us! After a while, I just had to laugh about it- I guess that if the upper Management wasn't going to stop them from ripping us off, I wasn't, either. They were always so nice and sweet, too- actually were proud of what "thrifty shoppers" they were.
DH works for a major Bed and Bath retailer, and is responsible for resolving customer complaints for his region. He gets some real strange ones! He recently had a lady become irate at a cashier because the cashier said Hello to the customer. The customer told the cashier that she was being condescending by saying Hello to her, and she was very offended and she'd never shop there again. WTH??

Whatever, lady!
He also had a complaint from a customer who was angry that the cashier had discreetly coughed (with her face turned away, into her arm) in front of the customer. The customer told the cashier she should stay home if she was sick. The cashier explained that she just had a dry throat, and the customer said that she had cancer, and her immune system was weakened, and she could DIE if she was exposed to any illness. The cashier apologized, and called a manager over to finish ringing the customer up, since she didn't want to accidentally breathe on her and her compromised immune system (wouldn't you think she should be at home herself if she was so sick that being out in public could KILL her

). The customer threw her items on the counter, and stormed off, saying that she was terribly offended- that cashier obviously was afraid of "catching her cancer" by not finishing ringing her up!!! Hello- you just finished telling her you don't want her near you if she has germs!! Geez!!
I am soooo glad I am no longer working customer service jobs- but I am glad I did for a while. Made me a lot more tolerant and understanding of the job cashiers, tellers, and waitresses and waiters do.