There is a avg 25% rejection rate as a result of propellerization and camberizing. The best practice is to purchase stock that can be returned for credit and up'ing the shopping list by about 25%.
I never really put numbers to it, but now that I think about it, it sounds right. Luckily, I'm done buying lumber for a while, but I'll file it away for the next project. Lowes is the closest store, and the next time I'm in there I'll ask them about their return policy on lumber.