Just make sure to note that provably fair is only as fair as the way you test it. If the test is done on the site that you're working with, the site may fraudulently state that everything is fair and legitimate -- but when you go test it on your own independent testing, it says that something is wrong.
So if you are going to be testing bets, don't do it on the site itself -- do it independently.
Normally, the site where you test fairness is a third-party one. But, I agree that we can't know for sure whether it is not actually connected to the site we are playing on. The good news is that we can indeed do the test independently, those sites are there just for our convenience, just like Bitcoin mining profitability calculator and similar things.
Knowing the hash of the server seed we can easily check whether it was tampered or not. And then, knowing the client seed and the server seed(unhashed) and applying an algorithm, we can check by ourselves what should the outcome of the roll (or the outcomes of all rolls with the current pair) really be.
