They operate like any other merchant. If he wants to make a sale you make him an offer contingent on the amp working as expected. You point out your concerns and ask for a return privilege or a better price if the amp needs work. He either says yes or he says no and you go from there. Yes, you'll get different tonality from a single 15" than you will a pair of 10"s. For the most part the 1x15" is a favorite of guy who play a lot of country and also play steel. The 2x10" is probably more of a rock amp. There are fans of both.