Yes, gambling sites provide us with server seeds that can be verified.
But how do we really know that these seeds are used in actual gambling process?
Isnt it possible they are just displaying server seeds and hashes that we can verify but in reality the server seeds they are using in the back-end functions of the game are actually different/rigged?
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.