It is not necessarily the bank that decides disputes. In the end it is VIsa and MC (because that is where the chargeback gets submitted to). I work with debit cards disputes, and in my experience Visa is easier to work with, while MC is more merchant friendly. The only time the bank decides is when it is something obvious (i.e. services rendered, unable to return the product, money owed, etc). For example, I declined a dispute recently because they threw away the product. We can't dispute for cancelled order if you throw away the product, lol! It is a requirement that for cancelled orders the product be returned.
But if the disputes department have submitted the chargeback it is out of the bank's hands. The best thing to do in a dispute is to respond to their requests: for chargebacks they are on a tight deadline, and if the disputes department does not get your response then it is in the merchant's favor. The opposite is true as well, if the merchant doesn't respond then it is in your favor. So if they come back and say, hey this merchant represented and we need this information... if you want your money back you'll submit that info, pronto. It gets submitted to Visa/MC again, and the final decision will be made by them.
In the above story I can only guess the merchant represented and gave proof that the cardholder was a part of the purchase (address, or some such thing). If the cardholder does not respond to the proof, or if their case "is not strong enough" (up to Visa/MC to decide) then it is a loss for the cardholder.
For the record I am speaking in regards to charges large enough where the bank won't want to take the loss. But my experience is only with Visa and Mastercard, and primarily with debit cards.
