Banks are pretty easy going about disbutes like this actually. I had a mail order place charge me a lot more than I agreede to pay for some film devolping. I called them up to ask about it, and just got transfered around and given a voice mail that box that no one every retured my call on. SO I tlked to the bank, filled out a form, and they retured my money.
Someone can make a claim, and false or true it's up ot the company to disprove it. A place where I worked once - a lumber store sold this lady some paint, the next day she comes back for an other gallon of paint. So when she gets her credit card statement, there's two identical changes one day apart. She calls up the credit card company, tells them that she only bought one gallon. So the store where I was working gets a call, says basically we have a report that you riped this lady off, you have two days to fax us proof that you didn't or you loose your right to take a visa credit card again. We had the copy of the reciepts where she signed, in person so no problem.
So this may not actually be fraud, but still it's really easy to get charges revoked if the consumer doesn't think it's legit.