if you want to be an elitist shop, then sure, but what about when someone comes in with a trek 820? or any of the other major manufacturers base model bikes? or any older bike? or a dirty bike? i think it's a bad idea. and it will only lead to conflict. how are you gonna say to some big redneck without insulting him that you don't work on bikes as cheap as the one he bought for his kid? if i was in some shop, looking to buy, and i heard someone get turned away for a repair because of the type of bike, i would walk out. hire some local kids to do the easy repairs, and try to schedule them so that you have time to do them. in the busiest season, up to a two week wait is not unheard of. of course, simple flats get squeezed in, but don't overextend yourself. book a reasonable daily amount of repairs for up to two weeks, then tell people that come in that you are booked for two weeks and really can't take in any more at the moment.