I am the one to use other's money and get 40%
No way there is no guarantee that you can be trusted and you will not run away unless you can do an escrow where you deposit money to an escrow and only released it when you send the other people's winnings, I figure this is another form of scam, how can you be so sure that you going to win the bet when it's a game of luck.
Escrow is important if there is a trust issues and also to avoid scam, because now a days there is a lot of scammer so, we need to takecare always to avoid scam.
When we never meet the person and we never make a connection with that person, it is better we use an escrow agent because that will be safe for us and that could prevent us from the scammer. We need to be careful in this thing especially if we want to partner with somebody we don't know and it's related to the money. In this forum, he can get many recommended escrow agents which he can choose to hold the money or the escrow agent can place the bets for us. If that is the case, we need to choose the right escrow agent who understand and familiar with the bets we want to place.
Prevention they say is better than cure, its better to avoid partnership deals that might lead to any trouble. Escrow cannot be completely trusted and I am glad you have mentioned how some scammers can work with escrow agents to make the deal look quite real and then end up scamming the innocent.
Although I have never done a deal like this but judging from the stories of people that I have read here on the forum, I can say that partnership deals are the most risky deals anyone would want to try, because both partners have never met and everything they share in common is based on trust and many at times, its discovered that one person is not coming in with genuine intentions and this completely ruins the deal.