welsher

A swindling better or book-maker on a race-track; one who absconds without paying his losses, or what is due to others on account of money deposited with him for betting. Also written welcher.

One who cheats at a horse race; one who bets, without a chance of being able to pay; one who receives money to back certain horses and absconds with it.

Alternative spelling of welcher.

someone who swindles you by not repaying a debt or wager