It's provably fair, not probably fair.
Online casinos and casinos that accept cryptocurrencies have to provide provably fair gambling and they have to write tutorial on how to verify provably fair on their casinos.
You can not trust them, verify on your side.
This is true for everything in our life. Everything is fair, until else.

As for me - i test online casino with small money. Deposit small, bet small, withdraw small. If everything ok - i add some more money.
And 1 more rule: when i bet - i forget this money.