If I have to trust reviews due to a game not having a demo, I actually check the gamefaqs user reviews. There's quite a few bad ones that are obvious fanboys or trolls, but generally if you compare the lower reviews to the higher reviews you can get an idea of if you will like it. I wouldn't trust one persons opinion on something if I had never met them, so I'll take the aggregate. The only thing that skews that is more obscure games which only have four reviews and they're all 8+, but for most common games I can get a pretty decent idea of what I would like about a game and what I wouldn't.