In cases like this, you should always let your gut feeling decide for you since it can take too long to notice that something is rigged. You can also take some snapshots or photos of that possible rigged website since they are using an un-hashed server. You can also test other websites Provable Fair algorithm.
Yes photos will be a concrete evidence if you decide to pursue on filing a complain. But make a clarification first to the developer because maybe it was unintentionally done and they can possibly compensate you with your losses especially if it relatively small. But making it legal would be needing an expert to attest your claims about it. So you will going to spend some money for it. How much loss you have made? Next time try to check those good gambling site for this.
You're right, especially when you're used to a particular online gambling casino with a mindset of them not be involved into cheat. I personally don't verify some online gambling casino websites before play because of my trust with them. Although this is wrong because any of these online gambling casinos can turn from their Fairless to be unfair just to game the gamblers. We should always ensure to verify gambling casinos irrespective of our trust with them to save others from getting be cheated like OP.
This is one thing that gambler should be consider. This is a lesson learn for every gambler. One should verify all things needed before joining into a gambling site. Pretty sure this will be a good experience being shared by OP.