A Schrader valve screams low end. I'm not even convinced presta works better but its a well known fixture on any bike meant for more than groceries. My guess is that your client could build the finest rim on the market, at the best price point, but if it were Schrader, nobody would want it.
Forget the logical arguments. It's all about appearance. If he's selling to people who at least think they're riding fast, presta. If he's selling to grocery getters, commuters, ride around the park with the kids, Schrader.