Honestly, I see a number of posts in several places such as casinos, forums (especially bitcointalk), and other social media, that is they say SCAM. When other people ask, how can they fool you? and the victim answered, I played this way blah blah blah blah and then I lost it shouldn't be because I used the method blah blah blah blah (until his mouth was foamy).
Hold for a while, user play and lose ?, user trading and loss. Then where is the SCAM? The answer is NOT a SCAM, but rigged.
I agree with you that if a person simply loses, it's a scam. But I have not really seen many cases similar to what you are talking about. Most of the time when I see scam accusations, they are related to a situation where people cannot withdraw funds from a casino or something. Another kind of case somewhat resembles those you're talking about, but they are different nevertheless. I am talking about people who were playing and kept losing against the odds (literally, when it's a game with strict odds but you keep losing). And these people might be right because it can mean that a website states certain odds when they are actually way lower, so people lose because of casinos being unfair.