Indeed, battling with demons is a sign that one does not want to be possessed. I'd be more worried if the possessed person did not battle them. The problem is that some of the voices can be from God, so Christians are easily possessed if they are waiting for God to speak to them. This is not a fairytale: there are many instances documented in the Bible of God, of angels speaking to people. Christians must guard themselves, because opening oneself up to hearing celestial beings, opens a channel to masquerading demons. However, demons cannot resist identifying themselves when asked. The advice I have read in religious texts is: When one hears voices, demand they identify themselves. If they are not Jesus himself, or a trusted emissary, then tell them to begone. In visions, follow the light.