A cult will have a slick well-rehearsed Public Relations front which hides what the group is really like. You will hear how they help the poor, or support research, or peace, or the environment. They will tell you how happy you will be in their group (and everyone in the cult will always seem very happy and enthusiastic, mainly because they have been told to act happy and will get in trouble if they don't). But you will not be told what life is really like in the group, nor what they really believe. These things will be introduced to you slowly, one at a time, so you will not notice the gradual change, until eventually you are practicing and believing things which at the start would have caused you to run a mile.
cult leaders will tell you can only be "saved" (or can only be successful) in their organization alone. No other organization has the truth, all others miss the mark. So it is not the belief system that decides your future, but it the belief system AND your membership with that particular group.
Be very suspicious of any group that claims to be better than all the others. A religious group may say that other groups following the same religion are OK, but they are the ones who have a better grasp of the truth and they are superior to the rest. This is often just a subtle version of exclusivism.
Cult leadership is feared. To disagree with leadership is the same as disagreeing with God. The cult leaders will claim to have direct authority from God to control almost all aspects of your life. If the cult is not a religious group then questioning the leaders or program will still be seen as a sign of rebellion and stupidity.
Those who control the information control the person. In a mind control cult any information from outside the cult is considered evil, especially if it is opposing the cult. Members are told not to read it or believe it. Only information supplied by the cult is true. One cult labels any information against it as "persecution" or "spiritual pornography", another cult calls it "apostate literature" and will expel you from the group if you are caught with it. Cults train their members to instantly destroy any critical information given to them, and to not even entertain the thought that the information could be true.
One of the most common forms of commercial cults is the pressure selling organization. These groups ostensibly make money by selling goods via their sales organization, but in reality they make their money by selling goods and motivational materials to their sales organization. Using mind control they seek to enlarge and maintain their sales force, and hence their profits.