Why do you void arbitrage winnings? You don't allow arbitrage on your site? Do you mean he bet on double side to decrease the risk? IMO it is acceptable.
Hi jujugoboom, I think you confuse arbitrage betting with "matched betting". An arbitrator bets on double "sites" and he "doesn't decrease risk", he takes none. No matter the match result, he will always have a small gain. Different sportsbooks have different policies about arbitrage, we are against it.