If there is a way to test if the provable fairness system works out mathematically and all outcomes and hashes etc are correct then there are no questions about it. IF you find that some of it is occasinoally off tho, then that is an instant red flag and the provable fairness becomes (probably fair lol).
Verifying fairness of the game is only possible on house games which is commonly open source and verifiable while the rest of the casino games from 3rd party is using RNG to determine the result which is close source. I believe this is what OP referring and there’s no way to verify the outcome manually if probably fair but this doesn’t mean they are red flag since these games undergo through audit before they have license to be distributed on casino.