Risk of fraud. Moving the money is not expensive, but if a $10k transaction turns out to be fraudulent then you're on the line for a big chunk of money. If you

Risk of fraud. Moving the money is not expensive, but if a $10k transaction turns out to be fraudulent then you're on the line for a big chunk of money. If you know your fraud rate is ~1%, then if you charge 1.5% on all transactions then over enough transactions you can cover the fraudulent ones and have some profit left over.