The only time I got upset as a customer was in Target. I bought one of the Isaac Mizrahi handbags a few years ago. I took it home, cut the tags off, unzipped it to put my stuff in, and the zipper broke.
I took it right back for an exchange (with receipt) and the manager was the rudest idiot I've even encountered. He refused to let me exchange the bag because he said the bag was used. I kindly explained to him that one would have to use a zipper to discover it was broken but all logic was lost on him. He just kept saying, no refund, no refund, over and over. I said I just wanted an exchange for a bag that wasn't broken. I explained how I didn't even get my things into it yet to use it for the first time, and he said, "Aha, so you admit you used it!" It was like talking to a tomato. I was so furious with him after five minutes of trying to have a normal conversation, I just left while he was mid-sentence. I bought it on a credit card that had protection, so they dealt with it for me.
I think my biggest letdown on the other side of the counter was when I worked at The Broadway. A guy came in and wanted outfits for his teen daughters and made me put together clothing choices for them and he wanted really high-priced items. He didn't know sizes or color preferences, or style. What do you do in that case? I picked two tops and pants and a cardigan that was popular (in two different colors) and of course, the girls exchanged them and took the money. It was a no-win situation but it made my commission numbers look really bad.