Depends on the dispute. If you understand the situations where you can prevail, they will back you every time. I'm about 95% with all of the claims that I've made. Recently, I disputed a software purchase that didn't function as advertised and the merchant simply failed to respond to any inquiries. Refunded.

My only failure was my attempt to dispute a vehicle shipping charge with DAS. They damaged the vehicle and wouldn't respond to any inquires on how to make a claim. The credit card company explained that the contract was fulfilled and that any damage claim is after the fact.

With the case of the lost bag, it appears that they didn't fulfill their end of the agreement and would not be entitled to the fee...........however, their contract of carriage surely must state otherwise, and, hence..........you lose.