If I could pay by card in your shop - I'd do shopping here 16 years ago
Certain shop owners fail to realize that managing cash (instead of plastic) is expensive too -- probably even more expensive than AMEX extremely high fees. If you factor in: counterfeited currency, risk of robbery, lost business, trip to bank to deposit/withdraw cash etc,, it's easy to see how expensive managing cash is. Here in Holland i'm actually starting to see shops that only deals with plastic and don't accept cash.