first, you're an idiot for buying a jet ski without checking it out. i think you ought to have taken the hit for jet pump.

second, if i were a buyer, i would not have accepted a check, becuase of douchebags like you. Everything has it's problems, and it's your job to discover them before you purchase the item.

Did the seller agree to accept less money for the ski? or did you just TELL him that this is what you are paying for it? Did you sign any papers when you handed him the check that stated what was paid for the ski?