Why do payment processors charge a percent fee on transactions?

Question

Why don't we have fixed fees per transaction? Do payment processors have to do more stuff to complete a high value transaction vs a low value one?In my opinion, the thing that drives cost for payment processors is the number of transactions, not their amount, so wouldn't it be fair to charge customers based on that?

ksaj · Accepted Answer

The higher fees subsidize the lower ones. If it were flattened, people wouldn't want to do smaller transactions because the fees would be too high by proportion.

ev1 · Answer

More profit to charge a higher fee on larger transactions.

trinovantes · Answer

Someone has to foot the bill for credit card rewards