GOG have updated their website with a host of options to sort and filter reviews. If you scroll down, you'll see 3 scores: all voters, verified owners score, and your custom filter score. Dragonspear has 2.5/5.0 from all voters and 3.6/5.0 from verified owners. BG1, BG2, and IWD don't have such a disparity: the overall and verified owners' scores are similar there.
Quite happy to see GOG add review options like this. I know I voted for some of the features. It'd be cool if they could eventually get a graph of scores like Steam has: You could easily see what times a game got negative or positive reviews.