How long does it take a check to clear and to find out if it is fraud?

I'm selling a car for someone and have alot of potential buyers. Most of them are offering checks and it's alot of money so I do not want to take the risk of cashing the check later to find out it was a bad check. So how long will it take before I'm sure that it's a good check?How long does it take a check to clear and to find out if it is fraud?
Depends if the check is an out of state or a local check...out of state could take over a week, local checks usually less than 5 days....your best bet would be for them to bring a money order or a cashiers check made out to you...those typically are a little more safe.....