If we want to stretch all the possible points of view to find acceptable cases, then there's just one case, if the shop has a no questions return policy that it's willing to fully use to attract customers, then no problem, but if you're exploiting a policy meant just to protect customers, then it's definitely wrong. BTW for the acceptable case, every now and then some shops explicitly apply a policy (Edit: actually this isn't even a return policy anymore, but a special offer) that lets customers buy the old model, then, when available, get the new one returning the old one and paying the difference.