As many members already mentioned this is a pretty common scam tactic on Telegram lately. I was personally also bothered with these messages, but to be honest, it is pretty obvious that this is a scam and everybody should recognize it after only a few obvious questions.
First of all, why me? If this is such a great deal, why he doesn't do it with family or friends?
He replied that he didn't want his family or friends to know because a few friends are actually working with him (so this is not possible) and he didn't want the family to know what he was doing. A scammer who is afraid of friends and family, but is not afraid to ask strangers online and to provide all details? Pretty dumb explanation, in my opinion, don't you think?
So, I told him: "no problem we can still do this business, despite I don't believe you, but you have to send me the money first (only for the first bet) because I am poor and don't have it right now".
Of course, he denied, so I ask why not? He has nothing to lose, he works there, he will help me to win, he can block me or don't help me to win further if I don't send the money back.
Nothing helped, he still denied, so I told him that now I will contact the casino and tell them about everything. Of course, I haven't because it is an obvious scam attempt and I knew it from the start of this conversation.
As you can see from this example, we have always to be calm and think twice when somebody advertises such an offer or we talk with people on Telegram which are offering insane returns, especially, if from the beginning the scammer tells you that this is not (fully) legal. Remember that in such circumstances the victim even can't report it to Police or somewhere else because from the beginning knew that it's against the law. Of course, you can report everything, but I think they would look at you, not as a victim only an impostor who had just been scammed and do nothing to help.
I got already many offers like this on Telegram and talked with many of these scammers, always after a few questions they finish the conversation and disappear if they only see that there is no chance to scam me. They don't want to lose their precious time. Sorry to say, but they are looking for stupid, young, reach and not experienced people to scam. If they see that you have experience and ask the right questions, they will run away ASAP because there are thousands of other Telegram users to try this scam on them.
Until today even one offer which was advertised to me (like this one) on Telegram wasn't real,
don't rush if somebody offers you a lot of money, especially if you have to pay first to get it .