can i write something on the back of a check to say that they cant com after me later from a car accident?
IF i write something on the back a check made out to the person i hit, will it count for anything? would they be able to ask for more money afterwards for damages if they accept it?
No, it will not mean squat. A check is a check. You need a separate written agreement. Imagine how silly it would be if I wrote on a check to pay my electric bill: "This is in full payment or all current and future electric bills from now until forever."