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).
This is a nice comment as some reputable casinos in games that are designed by them also called in house games they offer you all the seeds,hashes and everything to check yourself and people do not bother to question about these games as they know they are provably fair.
The problem is with third party slot providers for example which you have to trust them and also the casino has to trust them as they offer no hashes,seeds or whatever is needed to verify that these games are provably fair,so in here you either trust them or not,it is a personal decision.