You can ridicule it, or you can take it seriously. It wouldn't have been difficult for him to simply get his laptop and record the whole session with his webcam, assuming he has one of course. There's no need to ask the demon for a group photo.
I've tried demon summoning, it didn't work for me. So if Fatekiller can get it to work, he should make some attempt to gather evidence of some sort. Whether it's with an audio recorder, his webcam on his laptop, or his phone taking pictures. Anything is better than nothing.