Replying to Turnip #tenacious_turnip
I think Sam's justification was that Burt "agreed" to gamble the prize money. Despite the fact that Sam said it "wasn't real gambling" and eliminated people for arbitrary reasons as a joke. He was terrified to say anything against him.
When Sam talked about it later, he said if they won the roulette spin, they would have doubled down anyway. And then doubled down a second time too. Coincidentally, he talked about how he wasn't going to give Burt the prize money earlier.