A recent article entitled "Converting Bigfoot: The Gullibility of the Religious" addresses all sorts of issues as to who tends to be gullible...as well as just how we define that word.
The first question asked is "Who is more gullible, a liberal Episcopalian or a conservative evangelical?" The author suggests that the common answer is "conservative evangelical," even when "gullible" means believing in "Bigfoot, UFOs, Atlantis, astrology and psychics." The suggestion is that evangelicals are already gullible when it comes to religion, and thus they should be gullible on all topics.
Have these people actually met a conservative evangelical? Maybe they know different ones than I do. I my experience, they generally have very little belief in such things, which are more commonly labeled as New Age, and New Agers are generally seen as liberals.
But there's also the question of just what does "gullible" mean? In presuming that conservative evangelicals are gullible, one is pretty blatantly stating that their beliefs are not only wrong but foolish to believe in. Likewise, why does believing in Atlantis or astrology or psychics indicate someone is more gullible? It smacks of the idea that "people who disagree with me are not only wrong but foolish. My way is the only intelligent way."