That would be because at least some of the cash bypasses the cash register and the tax report.

Edit: alternatively they might not have same profitability requirement as other restaurants, because a cash-only restaurant is perfect front for money laundering.

And they're probably just not comparable restaurants on average.

My barber only takes cash. $18 for a standard haircut.

That's not because of card fees but because of taxes. They can underreport their cash income, but can't do that if the bank and card processor are involved.

Had some fun with the thought of a “Standard Haircut”: https://chat.openai.com/share/cd2948ce-2285-4491-b58f-877abb...