Who knows? Maybe the sites use some algorithm that detects martingale players to clean them out. Either way its very difficult to prove.
Don't martingale, and if you do. Just do it across multiple dice sites and then you will know for sure if its a legit losing streak or you were being cheated.
You could also verify 999dice rolls as well but that site is still rigged ...
That's true, I don't verify every one of my roll either but PD is fair and I trust this site, I haven't been too lucky there but that doesn't mean that the site is rigged.
Btw ranochigo Nice signature.