There are three big factors in this- Social compliance, gullibility and of course intelligence. Varying high levels of gullibility and social compliance make someone more easily manipulated. Since the advent of social media social compliance has been a huge need and people spend a good part of their days considering it. This affects gullibility since, to be accepted socially you must believe what the accepted social group does. Someone can be somewhat intelligent and forgo it because of fear of social ostracization but the more intelligent you are the more you're likely to have lower levels of compliance and gullibility.