Just choose pieces that you feel best about. There really is no 100% guarantee, but buying from a store that keeps theirs in tanks or storage bins will give you the best chance. My advice is no matter what wood you get, rinse it thoroughly, let it air dry, then bake it at 350 degrees for 30-45 mintues depending on the thickness of the wood. The reason you bake instead of boil is heat the wood to a higher temperature to kill anything that may be able to survive boiling temps.