Yess you are right that mate and The most known tricks for those scam casinos are they are offering small amount of bets and then you have a chance to win big amounts without asking anything, then after you won then they will have new rules which is what you said above once a gambler want to withdraw his/her winning then the casino make a thing that a gambler can not make his withdrawal. Or worst they will abandon the request from the gambler that he want to withdraw.
Most of the time when a casino is a scam and they do not want to pay they will argue that you violated their TOS in some way or form, and while you could be completely sure this was not the case they will never budge, as doing so will mean they are basically admitting they tried to scam you and now they are backtracking.
However while common sense should dictate that a casino like that will not last long, we have at least one example of a casino which has been scamming their customers for years and the casino still find ways to gain new customers somehow.
And that is a sad reality. Most people are not yet aware of these scams yet. They still fall for some sort of marketing gimmicks along with the online casino's bonuses that are often too obvious to be a scam but people still does catch those. Casino's like giving a bonus such as added hit rate when they deposit $100 dollars. Or just as mentioned b the OP, the casino's purposefully give you difficulty on withdrawing your funds until you gave up asking for it. Some closes some do not. Most reopens just with another name.
Yes your right that mate and that will happen if a gambler some have enough knowledge and And iQ because there are some scams casino who offered a lot of things and make a gambler turn their heads and try to play in that casino. And best example of that is there's no KYC and They offered small amount of wager and then you win 10 times or more in one bet which is pretty good strategy to catch the attention of the gambler and once a gambler will try and then he will win then he can not still withdraw his money because there's a KYc or else they will make and excuses that your account was cheating.
You or we all know that it is commonly said that "if a thing is too good to be true, then check it very well, because it probably might not be true", one way scam casinos get hold of victims is through greed, it is the same way many crypto investors fall victim to various types of scams through connecting their wallet to an unverified source simply because they were promised some really valuable airdrop, and the scammers, instead of giving the airdrop after the wallet have been connected and the claim button clicked, will turn around to zap whatever the victim had in their wallet immediately before connecting the wallet to their fake site.
It is the same strategy those scammers use in a gambling casinos, though in a different dimension since casinos are centralized, if all gamblers can stop being greedy and hasty, but patiently verify a casino and make sure they have all the qualities of a legitimate casino before they put their money there, maybe, we will have a safer gambling environment around us.