I have never encountered a demon (that I know of), but from people who have, I have heard that there are ways to distinguish demonic activity from other things, such as epilepsy, bi-polar disorder, etc... although sometimes it is not easy . People whom I consider reliable have told me stories that sound legitimate. However, many stories that I have heard or read about second-hand sound like the product of an overactive imagination.
In the life of Jesus, there are numerous accounts of demonic possession. But there are extremely few reports of demon possession in the United States (or other Western countries). Why is that? Some more charismatically-minded Christians might suggest that demonic activity in the West is just as prevalent as it is in other places around the world, but many Western Christians are blind to that because they are influenced by secularism and are not open to that possibility. There is probably some validity to that perspective, but I wonder if there are less reports of demonic activity in the West because the Devil knows that that attack strategy doesn’t work very well in the Western context, given the fact that the scientific-rational culture dismisses such manifestations as having other natural causes. Therefore the Devil uses other tactics to decieve and destroy (secular humanism, atheism, religious pluralism, etc).
But in Thailand (and many other non-Western nations), I think we probably hear about demonic and/or supernatual activity more because
- Many people have a supernatural / animistic worldview already, therefore they over-report spiritual activity, and
- There is actually more genuine overt demonic activity in those places because it is a working strategy for Satan to keep people away from the true God.
The Devil is a pragmatist, and since fear of spirits and supernatural power work in many contexts, that’s one of the winning strategies that he often employs.