The only way you can trust the system is if the server does NOT change the server seed after each roll (that's what Nonces are for). The server only needs to change the seed if you ask the server to provide the seed to you so you can verify the bets. (i.e: Prime-Dice does in fact implement this correctly)
I have been wondering about this too, why the server seed changes every roll (on free roll and multiply BTC)all other dice games I've played seem to implement the same as what primedice does
the server knows server and client (player) seed but player knows only "server seed hash"
this way server might be able to change/adapt his own seed to manipulate the outcome
I think you mean:
the server only knows the server seed but the player knows the "server seed hash" and client seed which they can change.
AFAIK that is how we do it.
https://snag.gy/W9JsGl.jpg
If you can explain to me what is wrong with that and what exactly Primedice do differently I'll ask wetsuit about it.