What options do you have when they won't?
Yes, verify the problem with the service if it does not provide an explanation directly, if they still do not provide an explanation then make a bad review of the casino that does not pay.
making a test withdrawal would be recommendable before depositing big.
This doesn’t really answers OP’s question as he is not asking about how to identify a fraudulent casino but he is interested to know the excuses they give to
justify their scams.
Besides, scammers already know about this tactic. So, they will let you withdraw small amounts to gain your trust. Troubles usually arise when large amounts of money are involved.
Indeed, the amount of money is decisive in problems like this, the bigger the money you want to withdraw usually the more complicated it is, and fraudulent casinos will deliberately make it difficult for you to withdraw money.
Small money will only be bait.