[PrO.GameR]

If it's a race, do as Vince said.
if it's a single one, when you are showing it to player save the distance to the checkpoint, compare it with player's current vehicle's speed or if it's none, check with fastest car's speed, estimate how much would it take for the player to get there, if it's less than that it's most certainly a cheat (you can't get to anywhere faster than driving infernus in a direct line to there can you?)
although just warn admins about it, don't directly ban them.