Merch fees and card charges for points schemes you never use. The interchange is bank2bank, all of it filters back into 8c extra for the coffee in many economies. There's no accountability for the cost/price difference here. How do we know what amount went in interchange and what swept up into the profit account?

Also banks package card services for others. You can't just open a bank because you're filthy rich like Apple, you have to pay a bank to do card stuff for you at least for a while. Every Qantas money card I've had came with t&c which showed a bank was in the loop. For free? I don't think so.

Arbitrage I'm thinking the home investor doing off market purchase thinking it's some other day trading schmo but I'm unconvinced the bank cannot play inside and do 10,000 share buys to sell pricey in 2 share lots plus the trade fee thank you. So per trade fees plus forex plus some arbitrage would make a nice snack one million times over.

But more generally don't merchant banks make money in large amounts by doing this for economies with a need for iron and a lot of potatoes but without iron producers willing to sell steel for spuds? Banks are the one who can quote a steel to potato interchange rate that makes everyone happy, bank included. McDonald's Russia wants to buy Idaho potatoes and you've got a Turkish affiliate who can do roubles to potatoes.. deal done. Tasty snack for everyone.

It costs money to store gold. Mattress companies charge shedloads to let you store your gold under their mattresses.

It costs money to make money. Far better to put it out to somebody who knows how to make money.