First was at Michaels. One of my items got scanned a second time as it was being put in the bag. (Super easy to do at Michaels. I did it myself too many times when I worked there.) Luckily, I was specifically spending a certain amount, so I was able to say "Er, something's not right here" before I paid.
Second was at PetSmart. I was getting collars and tags for my two cats. I was tired, so when the total came to just shy of $50 it didn't click in my brain except to think, "Gee, that was more than I expected..." As I drove away I thought, "Wait, collars were $6 each, tags were $6.50 each, and that only adds up to $25." So at a red light I check my receipt and sure enough, the dog food from the people before me had gotten scanned on my transaction as it was going into their cart. I went back, explained what happened, and got a refund no problem.
Third hasn't been resolved yet. I was still tired, so I ordered pizza from Papa John's because I love their Cinnaswirl dessert. Ordered on-line, but then I got a call from them saying they were out of the Cinnaswirl pies. Sadness! There wasn't anything else I wanted, so I had them take those off (I had ordered two). Because it was an Internet order, they had to cancel that order and resubmit it without the dessert. It honestly took about 5 minutes on hold for them to get that part sorted out. When my pizza arrived it was lukewarm as well as cooked and cut weird, but it was pizza and nummy anyway. Besides, it was about 20 degrees F out, so lukewarm pizza happens. However, as I was going to bed I realized, "Wait, my order had been $22, dessert pizza was $6 for the two, but my new total was $20..." Checked my receipt. Yeah, I had gotten the special when I ordered on-line, but they charged me full price when they resubmitted it. The other stuff is no big deal, but I'm trying to get out of debt, and that's my dang $4! I'm going to be calling the restaurant today when they're open to sort it out.
EDIT: Argh! I just checked my bag from Michaels. The item that they double-charged me for? Not actually in there. Apparently it never made it into the bag.
EDIT 2: Sorry, it looks like I wasn't clear enough. The desserts had nothing to do with the special. The special price was only for the pizzas themselves.