A "Martingale" is a failure betting fallacy, and a casino can only hope for players so stupid. It will result in a player going bust far quicker than the casino.
I can believe this. I played over a thousand rolls this past week alone in the 50% bracket. I always start out with .05 BTC, and I've gone on 7x losing streaks (Lose .05 -> .10 -> .20 -> .40 -> .80 -> 1.60 -> 3.20) about a half dozen times. However, after looking at my trade history, I've NEVER gone beyond 5 straight wins, ever. 50% my ass.
You are welcome to verify each and every bet using the verification method described on the site. Smarter people than me can tell you why that's legitimate.
I also welcome you to do a scan of the 50% bets that have ever occurred, and see if the results are significantly off from what they should be.
I'm not trying to belittle your pain, I feel you. Lost lots of money on the Sex and the City slot machines in vegas last week

(true story)