Anybody can sue anybody for anything. Its not a question of someone being able to sue. Its a question of whether or not they can win. If someone who buys a piece of jewelry is ridiculous enough to sue for something that happens AFTER they purchase the jewelry and is a direct result of their own action (in this instance, leaving the jewelry lying on the table) then you will have to deal with the lawsuit whether its your LLC that gets sued or you personally, therefore you would not be shielded from the inconvenience of such a suit. However there is virtually no chance that the purchaser could win such a suit.
And even if you were to lose such a suit, your LLC would still have to pay the 500.00. So, if you are in the 25% tax bracket between state and federal taxes you would probably have to pay around 500.00 in income tax to shield you from personal liability for 500.00, but your LLC would pay it anyway...so you would still be out 1000.00.