Those suspicious things will depend on the casino, although we do not try to do any suspicious things that can make our account on their watch list.
The shady casino will use many ways to trick their members because their purpose is to freeze the account so they can possess their funds without having the intention to refund the balance.
It already happens to some people and even if they complain to the site, the site will easily ignore them.
So only research will help us avoid this thing so we can play gambling without worry.
Casino is centralized party, all you need is picking the reputable casinos first since you need to trust the casino with your money. Same like when you invest in new project or lend your coins, you need to trust the project/sites and understand what's the risk behind it.
If you choose shady casino e.g. 1xbit you have no hope when something bad happen to you. Even they're online and active everyday, they will not resolve your problems. So never play in shady casino and choose the reputable ones.