What Happens If You Cash A Fake Cashiers Check?

I Have A Friend Who Found Out About The Frauds Made By Cashier Checks. He Was Sent A Check For $5,ooo. Much More Than The Item He Sold On The Internet. The Scammers Tell Him To Wire 4,000 Dollars To Them Through Western Union. He Found This Was A Scam And He Is Thinking About Playing Along With Them And Cashing The Check At Any Local Cashier, He Doesnt Have A Bank Account, And He Wants To Know If He Can Go To Jail For This Or If He Will Just Have To Pay The Bank Back... Please get Back.