Although you should always play in a "fair and secure", or at least "fair" casino, you may find yourself playing in a casino that does not meet any of these criteria. If this is the case, make sure you are very careful not to break any of the rules.
A small example: most casinos only allow players from certain countries to play or take advantage of a bonus offer, as indicated in their terms and conditions (T&C) or bonus T&C. This step is checked when the player signs up for "fair" and "fair and secure" casinos, however, not all casinos take this approach. Some allow you to create an account from a restricted country or receive a bonus you should not be allowed to receive, then play, but when you try to withdraw your winnings you are unable to do so due to breaking casino rules.
Restricted countries are one of the biggest problems with casino restrictions, so it is recommended that players, in addition to reading the T&Cs, contact the customer service department and confirm whether they can play from a specific country, or receive a specific bonus. Keep the answers, as they may come in handy later.
Also, casinos that do not meet the "fair gaming" criteria may have some unfair rules in their T&Cs and may even apply rules that are not listed. In addition, these unfair casinos often look for excuses not to pay out legitimate winnings to players who have done nothing wrong.
In short, pay attention to all the rules and follow them closely. Ideally, take screenshots of relevant information such as T&Cs, bonus T&Cs, transcripts of conversations with customer support, emails from the casino, etc., as these may come in handy in case of any dispute with the casino. Of course, the best thing to do is to find a better casino and play there.