What does reliable mean? You want the crowd’s rating of the movie to align with yours, which is pretty much impossible. I find Letterboxd ratings to be more sensible than IMDB’s, so that is what I use. But I also read a few positive and a few negative reviews to get a better idea.
There is a site called Flickmetrix which has advanced filters and also an average ratings (critics, metacritic, IMDB, Letterboxd). Maybe that would be helpful to you…