-snip-
When someone gives you their account email and password, you will have full access to their account and can transfer funds to that account using other methods. So why would anyone give you access to their account with their funds?
Well I assume you are an honest person. And I also accept your condition that you will gamble using my funds and account and i should pay you 50% of my total profit. But if you lose my funds while gambling then who will take the responsibility of that money? Will you take responsibility for 50% of that lost money? As you are ready to take 50% dividend ?
I bet he isn't. If he wins he'll split the win with you (probably). If he loses he'll disappear. That's his way of making a safe bet that he cannot lose.
I know a lot of guys like that who would bet wit you or borrow things from you and when they lose the money or break these things they don't want to talk about it anymore, act like they'll pay you back later but it never happens.