I believe there are known people in crypto that gamble in Rollbit and Stake regularly without problems and that have also vouched for them. One of them is known for his Twitter username as "KeyboardMonkey". I believe he is just one of the few real professional traders that has truly made large profit through trading cryptocurrencies. There's also another Bitcoin whale mentioned here in BitcoinTalk that gambles in either Rollbit or Stake, called Gainzy.