They can’t add sneaky code to the process (without getting caught). For sensitive game code every single change needs to be tracked and reviewed by the authority. You get audited at least once a year, and then all the changes are reviewed. Authorities outsource the job for the technical reviews to specialized companies.

Also, what’s the point? The games already provide a margin to the host, why risking to go out of business for such an irrelevant gain (a few more %)? Add to this that usually casino games writers do just that, write games and sell those to N casinos. So the incentive for the casino games writers are even smaller.

Finally, yes you can write “license X”, but you can cross-check that information from the regulator itself, you don’t need to trust just the line on the site. The point is you as a customer can choose a trustworthy site, ideally one who is licensed in countries where regulations are quite tight (in Europe I would say Denmark), before putting your money somewhere.

At some point you need to trust “someone”, that’s how the whole world works. The gambling authorities are no different than the authorities that enforce the safety certifications for electrict equipment, or cars, or whatever.

If your concern is that you would lose money on casino games because the site rigged it, it’s a relatively silly concern. You will lose because the casino games are designed to make you lose in the long term, on average.

How can players be sure they are honest?

At the bottom of each gambling sites usually there are the banners for the license(s) the company holds. Complying with licenses (e.g., Maltese) ensures that the due paperwork (i.e., proving that Casino games are functioning according to their certification) is taken care of. So yes, national gambling authorities usually are the ones who protect people from scammers.

They run rigged games in predatory ways.

I don’t know what you mean by this. Games have a fixed margin which is usually disclosed or can be computed (exactly like the 0 and 00 in the roulette skews the odds in the house’s favor if you want to do just black/red). There are then whole chapters in national regulations about random number generators to ensure the odds are correct and the games are not rigged (i.e., a game certified for 98% should have that outcome). Are games designed to have the house win a 2,5,7,9% margin? Sure, but this is out there in the open, there is nothing to “rig” in the same way having 0 or 00 is not “rigging” a game of roulette.

They happily let organised crime launder money for a cut.

At least in Europe, you get audited quite often and AML regulations are very tight. Laundering money via online gambling companies with their cooperation seems quite unlikely to me (and inefficient, possibly, but I don’t know).

They fight regulations designed to reduce problem gambling.

Some do, but not all, and not in all cases. Addicts are bad for business for gambling companies, or at least for some of them, moderate long-term customers are generally better (and require way less effort).

I don’t know what you know about gambling, I definitely think that the ethics are questionable, and I left the industry when I could also for those reasons, but the company I worked for was not very bad in this regards. Maybe you worked/had experience with some of the shady ones (like those who operate in illegal markets using a single license from a random tiny country)?