> It's common here in France for credit card operators to have fees in the 5-10% range (or 0.30€ per operation + 2% of the amount)

Interchange in the EU is capped at 0.4% for credit cards. Typical costs for processing are much lower than 5-10%.

For example, Adyen charges the 0.4% interchange + their fee of 0.6% and a flat 0.11€. On a 10€ transaction, that's 2.1%.

In most cases this is cheaper than handling cash. When you accept cash, you have to pay somebody to close and reconcile the drawer, take the cash to the bank (or have a security company do it for you), account for shrinkage / mistakes...it's a bit of a myth that cash is cheaper for businesses to handle, especially in places like the EU where card interchange rates are highly regulated.

Now of course, if your cash is not going the usual routes and isn't getting accounted for in the books...that equation can change.