My usual mode of collaboration with others is like this. If the profit you expect from me in a game is assumed to be 5000U, then I will pay you 5000U. If lose the game, you will compensate me with 5000(i paid you before)+5000 * 1.3=11500U, and all transactions will be made using escrow to keep ensure the fund security of both parties
So you will be looking for compensation cause you stakes higher that the amount you were expected to pay the other partner should the game have been successful.
It's some shady business, but you're looking for someone who is already into fixed matches so it should not be shady to them at all and they're rising nothing from the start so it's a good way to show they actually do trust the games they provide.
How do you plan to find a escrow you and the other party will trust?