The game is that if you refuse, the person loses their $999,999.
It's pure evil.
Neither player has any right to the money until the game is over and the game isn't over until they've both made a decision. That's the difference between this game and a millionaire offering you money. You may be lucky to be offered anything in both cases but in one you are being screwed in the context of the game. It's a matter of returning the favor. It may not be the most economically sound decision but if the amount lost isn't significant to you, it doesn't matter.
> It's pure evil.
"markdown took $99 of $100?! He caused me to lose money. He's pure evil." No. It's not my money to lose but I don't like the way you played the game so I'll pass on the $1, thanks.