The only source I can cite with any alleged experience in these matters from a Christian perspective is the Roman Catholic Church.
Before I continue, I want to reiterate that I am a Jew. Jews are not in the business of making converts, proselytizing, or actively adding members to our religion. I am also not advocating religion as a panacea or claiming that Jews hold the Roman Catholic Church as the authority in spiritual matters. This is only to add some educational data that might be useful in answering the question posed. No intention is made to suggest that the following information is the "ultimate truth" in the matter.
While Judaism has some demonology in its theology, it is neither universal to Jewish religion nor embraced by every Jew. However some of the basic theological principles did transfer to Catholicism.
According to Catholic teaching (and insight I was given by a priest who served in the past as an exorcist), the Catholic view is that actual possession (an extraordinary and rare situation in that religion's views) is always invited. It never, ever happens to someone who is not in one manner or another dabbling in some activity in which interest or desire invites contact.
The contact can begin quite innocently through curiosity, and the very few "genuine" cases on record seem to have that as an earmark. But, interestingly enough, the Church makes claim to so few cases of genuine demonic possession that it is almost non-existent. This does not mean exorcisms do not occur, as quite many indeed do today, but that rite is not merely the ritual expelling of a demon that has possessed a person, but more often a demon that is harassing a person. The blessing of an object for a holy purpose or to protect it from evil is also an exorcism.
The rite to expell a demon possession is not performed until all scientific explanations and medical procedures have been exhausted. Occasionally the rite may be performed on a mentally ill subject who merely believes they are possessed when medical professionals believe it can help the same. But subjects who claim possession are medical subjects first and a!ways until such a time as no explanation is left and signs are met that theologically fit the pattern of possession.
The Church does not release details about cases and more often than not hides the identities of the current exorcists in practice. Demonology suggests that demons recognize a hierarchy in Christianity, wherein lesser demons can be exercised by some denominations but others require longer standing (older) churches or denominations. This seems to be the unspoken rule recognized by the churches as well for when some churches fail in a possession case, regardless of the formal views they may have about the Holy See, the Catholic Church is always contacted for the most severe cases. Apparently, as demonology suggests, some demons will only be exercised by the oldest Christian authority.