Apparently it won't be, since some people here seem to think stealing from its users is a commendable practice.
Seriously, how would you handle the case "someone sends an unconfirmed TX right before the bet ends, TX confirms after the bet has been decided" ?
Refund?
You want to discourage scammers, not have to guess every time whether the request is legitimate or not.
Just add a reasonable fee for this kind of refund, it is more than enough to keep scammers away. Charge, let's say, 5% of the amount received. There is also the case "someone sends a transaction not so right before the bet ends, TX confirms after the bet has been decided", refund at 5% fee, too, obviously.
I can't even start to understand why you think this is not the proper way, and stealing is the correct choice. MP really got a legion of fans.