Something similar happened to me last year I want to share, when I was at Toronto at a store(forgot the name). The guy at the counter swiped my CC three time... yeah three times. I asked him why three times he gently replied that my card wasn't accepted for the two times and added, it may be due to wearing out of card(he was right. It was much used). I believed his story and came back home and there was nothing wrong with the bill, when checked later.