Instead of other sites where every place gets 3.5 stars, we come up with our scores using the same Foursquare magic that powers Explore. We look at signals like tips, likes, dislikes, popularity, loyalty, local expertise, and nearly 3 billion check-ins from over 25 million people worldwide.
Dental professionals are especially vulnerable to malicious and or abusive reviews and corrupt review sites.
Based on the linked article it looks like Foursquare is developing a system that does not rely solely on what people are willing to write but tracks actual behavior to determine a quality ranking. Good start.