If they show the hashed seed before you bet, and the process using the server seed (provided afterward) and your client seed results in the output along with their server seed hashing into the hashed seed then it's perfectly verifiable.
Suppose my server seed is X and the result of it and your client seed would be tails (in a head/tails game).
I then hash the seed with SHA-256 and show it to you publicly. After you bet I reveal the server seed and boom: you can verify everything since I can't lie about the hash.
Please correct me if I have made an error in any way.
You are correct, but my point is that: is the "hashed seed" they show you, really the seed used to run the game?
for example they can just generate a random hash seed (asdbfj891y23basd) and display it on their website but then actually, their game will use a different hash seed (138sdf71982789zcxz). then when you lose, they will of course show you the server seed which solves your seed. but in reality it is totally different.
The way I see it, the seed and hash they provide might be legit, but what I feel is a source for worry is that of some dice sites having to ask players to first click some tabs to be able to see the hash. That may well be a knock on the door to alert the occupant to tidy things up before letting the one at the door in and all the while he stays, every thing would be made to look straight. I think having the hash to stream along as the game is played, should be a more convincing way a site should show they are truly provably fair since their code is not open source.
This is the reason why people need to learn how provably fair works because many have no idea how it works exactly and always assume a casino can cheat but they don't understand that the rolls are already determined before the bet is taken place.
I don't think any casino would do what he suggested, showing one seed and using another because eventually someone would of caught on and complained, they don't know whether who or not actually verifies the seeds.
I am one of those who didnt know exactly how provably fair system works. This stuff is beyond my knowledge. But, I am very sure that there are a bunch of people out there who knows exactly how this stuff works. And if something went wrong with provably fair, I do believe most of them will inform it to us.
Basically it works like this
You are given a server seed that is unhashed like "ZYX", lets assume the hashing method here is SHA256.
The bet usually takes the server seed + client seed + nonce.
Client seed is usually also something randon but you can alter it anyway you want. Lets say client seed is "321".
Nonce usually refers to the bet # at the start of the session and just increments by 1, very similar to bitcoin block hashing.
So your roll result will be something like "ZYX3210", "ZYX3211", "ZYX3212", etc, etc. That number is usually in hex and modulus is taken and its rounded so you get the result like "98.35", "82.34", "24.42".
So now that you know this you think you can predict the outcome correct? No because the ZYX is the unhashed seed which you are not given until the end of the session. The hashed seed of "ZYX" is "ABC" and the "ABC" you are given. This is just given so you can verify that they never changed their unhashed seed on you.