They are providing the buyer the service with an echeque, so I think they should pay.

But don't buyers essentially pay the fees regardless of funding source, anyway? As a business, I'm sure you factor the cost of using PayPal into your prices and so forth, so when buyer does pay with PayPal, you still get the X amount of profit you want...so wouldn't that just make it more of a case that you want them to be more aware that they're paying those fees if they use an echeque?