Although it is difficult, rather impossible, to get any sort of guarantee, you might keep the following in your mind while picking an online casino:
Is the casino ranked high on major search engines for relevant keywords? If the answer were yes, then it might mean that the casino is well linked and popular. Common sense dictates that a blatantly unethical casino that is doesn't provide ample quality and security checks will not be popular and ranked high on any search engine. This isn't a sure-shot method but you may use the SERP ranking to shortlist the most popular online casinos.
There's nothing better than 'word of mouth' validation. Pick online casinos that can come highly recommended by friends and acquaintances. If they've played online or maybe if they know an individual who has played online and come back with a positive experience, chances are, the internet casino they have visited is safe enough.
Look for security and privacy related links which provide some information regarding SSL or digital encryption technology employed, and security processes followed on the site. An online casino that gives out relevant details about the security, names valid technologies from trusted sources (like Wager Works, Microgaming, Playtech, Cryptologic) and defines its security processes is most probably serious enough to be regarded as an option.
Check out options like flash casinos. Since you do not have to download and install any software, the possibility of jeopardizing the security of your computer is lesser.
Check out sites which provide feedback and ranking on online casinos. You might want to rule out any online casino that is being consistently bad-mouthed.
Read extensively. Try and find information regarding technologies employed in online casinos and the degree of protection they provide. It seems sensible to put in time and effort to make an intelligent choice before you start rather than regretting later.
While the above only deals with avoiding the occasional rogue casino, sometimes it's the players who are deceitful or irresponsible. Among the most common cases is a player who signs up for multiple accounts at a casino using fake names to reap the bonus more than once. Another player might use Adobe Photoshop or possibly a similar tool to manipulate the graphics of a slot pragmatic gacor machine screenshot to try and fool the casino into believing she hit a jackpot and didn't receive money for it. These are invariably gross violations of the terms of service of casinos and are not tolerated. They usually lead to locking up of the account or accounts of the player responsible. Some casinos even have a policy of informing other casinos and software providers to keep the player out of other gaming portals.