Alas, it turns out that the double-down strategy, although deceptively appealing, is no different from other roulette bets: In the long run, the gambler will still lose at the rate ofR$.053 per dollar bet.
Yes, the Martingale strategy is legal on betting sites. This strategy, which originated in 18th-century France and is commonly used in games of chance that offer a 50/50 bet, involves doubling your bet after each loss so that the first win would recover all previous losses plus win a profit equal to the original stake.