yea ive kinda had this prob too, what to do when you are handed your sack, but u dont exactly know if its too little, or if it is what to say, or something...i usually just go, "dude if ur fuckin me over im gona be pissed" and then they usually re-assure me, then i take it home and weight it, then if its off ill be like dude u undercut me, and if they appalogize adn give me more or something then sweet, but if not i get somone else.