It doesn't really matter because the customer isn't on the line. It's PayPal that is. Considering how fanatically PayPal fights fraud, that they don't consider this an issue pretty much tells you that it isn't one.
Sure the customer is on the line. You make a very large charge on a customer's credit card, and best case is that they can't make further charges on the card because they've hit their limit. Getting it resolved in a week or so is little consolation when you have a useless credit card.