No they can't. If you think your scheme is fair, then let's play a game of 'heads' or 'tails' using your provably fair scheme. If you correctly guess the outcome, I'll give you 100 BTC, if you lose you have to give me 10 BTC. We can use Dooglus as escrow.

So let's use your exact scheme:


Probably Fair Hashed Shuffle String:   2f35ca84adb6daa7bd2ca1a755bbf6e26caf9f822e6079e8c70e96ae1099b383


And to follow your protocol, you'll need to give you move ('heads' or 'tails') along with your client seed.



And then I'll reveal the final outcome. If you guess correctly you get 100 BTC, if you incorrectly guess you'll have to give me 10. And to make it "provably fair" and follow your scheme i'll reveal my "initial server seed", "salt"  and then of course, the "final seed" (which is derived from an unknown (for security), but deterministic algorithm).



If you are unwilling to play against me (using an escrow of course), I think it's rather hard to argue you casino is provably fair...