As an engine builder I would say your right on track. Used factory cranks are subject to condition and sizing. If they are undersized it is possible to have been damaged and have a hair line crack that is not noticeable. If it is std. size it may be worn and need to be turned to get back to a usable size. all of this must be considered when purchasing a used crank. New forged cranks from Eagle or scat cost more but are usually 4340 material which is much stronger than the normal 1053 material that is factory. Good luck
