There is a saying that goes by "Never attribute to malice that which is adequately explained by stupidity."
I do think that the vast majority - if not all - complaints are genuine in a way that the person complaining feels like they got cheated/mistreated by the casino. I am sure the feeling itself is very real, although there is a high - about 50% - chance that the complaint is actually invalid.
Can't we say that it is malicious that some people are making accusations because they want to harm the casino? It is no less evil if someone does it because of some dissatisfaction after losing money in the casino. There are people with real issues and ones with invalid complaints, but I just wish to remind you about the third group of "paid trolls & people who can't accept when they lose".
I would not call it malice or evil per se. I consider an action malicious or evil if the purpose of the action is to hurt, and I do not think that is the case here. Making a negative review or a public complaint will negatively affect the reputation of what the review is about. Does it mean that every negative review or complaint ever made is malicious or evil? I do not think so, yet all of these affect the product, experience, or business negatively. The purpose of these actions is not to hurt but to share an experience, rant, validate their feelings, or—especially in the case of online gambling—to get someone to look at their issues and resolve them. The purpose is not to hurt; it is just a side effect. Although it definitely helps as casinos only care about their profits, which correlate with their reputation. So the mere threat to their reputation makes them more likely to spend resources to resolve the issue instead of just ignoring the player forever. Of course, proper oversight and regulatory authority -if there were such- could also enforce issue resolution through either fines or license revocations.
I would definitely not treat paid trolls and people who can't accept losing in the same group.
The latter group is emotion-driven; they want to rant, get compassion, and believe that the house cheated them because otherwise, they would need to face the sad reality that they just gambled away the rent money. The purpose of their complaints is for them not to feel so bad about themselves, not to hurt the casino, although that happens as a side effect.
The former group is malicious; their purpose is to hurt the reputation of the casino. I just thought about it, and this group is supposed to have the most resources. It makes no sense to me what many forum members believe — that the vast majority of complaining new users are part of this group: trolls whose purpose is to hurt the casino. They have the resources to either buy or "grow" credible accounts and use those for accusations and complaints. Why would they go with fresh, low effort, totally uncredible accounts?