If you lose to a bet, there are ways to verify the result of the dice. I'm sure you have found how way to learn the provably fair system which most casinos will provide the encrypted hash. Here's a good page for it www.provablyfair.me/verify-bets/

There is also this thread here seems to have detailed it all regarding those seeds. https://bitcointalk.org/index.php?topic=5227525.0