I've spoken in-person with Google Maps engineers multiple times in the past few years and they all insist that Reviews and Ratings don't impact rank.
However, I think it's possible that they may have been mostly referring to whether reviews are positive/negative or high/low. I think it's possible that the quantity of reviews does have some influence -- more reviews, whether good or bad, could indicate relative popularity. And, if the reviews are from sites where Google has a higher level of trust that the reviews are less-gamed.
But, rmjvol is pointing in the right direction as far as I'm concerned: there are a lot of different factors which appear to influence ranking in Google Maps and the 7-pack, so you need to consider all the other factors involved.
Just two "for-instances":
- Citations have appeared important to rankings in the last few years -- is the business mentioned with some frequency in various places?
- Could the site have lost a valuable inlink in the recent past? Maybe they participated in a charity event last year, and didn't this year, thus losing an important link from a .ORG site or somesuch?