Everyone can mistakes, but their's was being rude! I always try to judge what I'm spending, and if the bill different than my estimation, I try to look at the receipt before I leave the store - not just at the fabric store, but at the grocery store or Target - whatever. I've felt sort of rude sometimes checking up on them right after the sale, but so far, no one's been rude when I called a mistake to their attention, and I'm still in a position to "prove" I was right.