How do credit card companies deal with disputes of duplicate charges?

Question

I recently read a post on another site about this situation, and was wondering, as a general question, what stops a merchant from (inadvertently or deliberately) providing multiple copies of documentation that relates to the single legitimate charge as evidence for the duplicates that have the same date and amount. And are you required to determine which one was legitimate (to exclude it from the dispute) and which ones are duplicate, or can you just pick one?

On the post I read, a gas station had charged four times for the same gas, the customer disputed three of them, and then the gas station disputed the chargebacks. In the discussion following this, it was suggested that the gas station disputed the chargebacks by providing multiple copies of the documentation relating to the single legitimate charge (i.e. proving that the customer did buy this much gas - once), maybe without even realizing it (if they were contacted separately about each chargeback).

My question is what mechanism credit card companies have for detecting/preventing this from happening, since surely duplicate charges are a very common form of error.

Answer 1

If the gas station could provide four different signed slips (different mean different timestamps and sequence numbers and also different authorization numbers which match the ones in the transactions - for the automated machines where there's no signature but the card is present) - then the station could have proven that there were indeed four separate transactions.

Otherwise it cannot. Duplicate transactions are easily disputed and a merchant will rarely try to dispute the chargeback, mostly for the reason that they have no proof of a separate transaction. Which one you chose to dispute doesn't matter. If you claim that the transaction is duplicate - provide the one that you consider original, and the credit card company will sort it out.

Usually merchants cancel duplicate transactions when you contact them, since chargebacks cost them money. But if the merchant is stubborn/dishonest/doesn't care - you dispute and you get your money back.