Just wonder how will you check it? You decide to check our honesty - you check the client seed, remember it, you make a bet - and check what was the server seed - seems ok? But it isn't in this scenario we could just easily fool you by using any seed that will make any outcome we want - just enumerate few random seeds that would give us desired outcome. Even if we would somehow publish a hash of this seed - you cannot be sure that hash you see is for the seed that you will get when you bet, since any other player might use this seed before you.