This warning comes from Police Scotland. The victim receievd a letter asking for someone to place bets on behalf of the sender, for which the victim would receive commission.
Think about it. Why would anyone need you, or me, to place bets on their behalf? They could easily place the bets themselves either by going to a betting shop or opening an account with an online betting site.
This is a variation on the classic scam where people are asked to receive money from customers and forward it to the scammer. You appear to be making money, you forward the money to the scammer only to find that the original cheque/transfer was fraudulent and you are left out of pocket with no way of claiming your money back from a scammer who has disappeared.