We accept credit cards but only if you are buying over $100 (10,000 yen) worth of wine etc, we get charged 7% by the Credit card companies, it is really a rip off for small merchants here in Japan. The large retail giants they pay only 1% or so, but we are NOT large, so we get stiffed. I've had customers from Hong Kong or Singapore come and buy a LOT of wine, say $2500 worth, they always ask if they can get a discount if they pay cash compared to the credit card, I will happily give them a 5% discount for cash.
I don't know the laws there, but I'd say if he is complying with the law, and being very open about it, what is wrong with that?
He may only pay 1.5% to the credit card companies, but then I would bet that he has a lot of other paperwork that has to filled out, and that costs him time, or money if he has to pay someone to do it.
By the way, we are paying about $7.56 per gallon for gas over here in Japan, and that price is nothing special, it was higher a while back, but has come down a bit.