some pepole can be pretty good at it me and my buddies use to sit around guessing the weight of bud and different objects but i would never let any one weigh my bag by eye balling it . unless its your bestfriend and you know hes not out to take your money . i also knew a kid in high school that would go around saying he didnt have a scale so stupid kids would fall for it lets just say that kid made alot of money.