There is only one thing we can do - expose them wherever we find them to the authorities. Reputable airlines do check, but there are some who don't or don't seem to care. You can bet the insurers will care if a faker causes a claim and it's found in the subsequent investigation that they don't have the required hours for a command!
Here's a good example.
Express.co.uk - Home of the Daily and Sunday Express | UK News :: Cheating pilot’s new career is flying high