* If tomatometer & audience score are within 5% of each other, you can trust the ratings to give you a decent indiciation of movie quality.
* If tomatometer is more than 15%+ higher than audience score, it means it's an artsy fartsy movie that critics like and movies don't.
* If audience score is 15%+ higher than tomatometer, it's a fun movie even if it's not oscar worthy. (https://www.rottentomatoes.com/m/old_school is a perfect example)
* Overly artsy
* Overly political. Reviewers feel the need to give it a positive review because they agree with the message, while the audience will split because they're not as homogenous politically.
* Outraged fans. Reviewers aren't typically fans of a given franchise and so won't notice if it ruins something that would irritate a fan. The Last Jedi is in this category.
* Bribery.