If the check was not cashed or deposited, then you would to replace it (since in this case, payment has not been made), but first may make sure that it is not cashed or deposited. Not only should you check with the bank to make sure it's not been cashed, etc. to date, but only have the bank void or cancel the check as having been lost. Only after you are sure that it cannot be redeemed would you have to replace it, and you could reasonably charage the cost (i.e. any bank fees) of doing this against the amount you remit to the buyer.