In my experience timber merchants usually offer the best quality timber over the builders merchants like Jewson & TP, who in turn are better than the usual sheds. If buying a large quantity of timber slipping the yard man a fiver, for the extra effort of selecting the timbers gets results. If you are having a delivery then you are in the lap of the gods, although I have witnessed a joiner reject a load of studding because quite a few lengths were banana shaped. I suspect if you manage to read through the small print in the terms and conditions you may find the supplier reserves the right to supply a certain percentage of out of spec. material which might cover the banana shapes.

Richard