A believer can be decieved yes but that is not the same as being possessed or having a demon inhabit them. we are likened to being the temple of God and so can darkness exist in his temple where his presence resides? I have never seen this in scripture and so I have no reason to believe it is possibleThe key word is "willingly". Why would Adam have willingly eaten of the tree of knowledge unless he had been deceived? Or are you claiming that a Christian cannot be deceived? Remember Genesis 3:1 and the outcome of an act of deception or the warnings issued about very human con artists, how much more effective can an entity that most people cannot detect be when whispering in one's ear, and acting to arrange events to support the "warning" whispers and offering guidance to avoid the problems.
Also what you are referencing in Genises is before the viel was torn and before we became the temples of God Adam eating the fruit and inviting sin is also not the same as a demon coming into him so that doesn't really show any evidence it is possible either