Examples:
- if a person only posts 5-star or 1-star reviews, they are polarised and/or punitive. Any and all reviews from such users should be weighted accordingly - 5 stars clearly means "thumbs up, for whatever reason" and accordingly 1 star means "thumbs down, for whatever reason".
- if a person posts a fair selection of review scores, they are likely more thoughtful. Individual review scores from these users are more accurate.
- if a person posts mostly 2/3/4-star reviews, then any 1/5 star review is likely to carry a lot more weight.
To make score manipulation slightly harder, some kind of meta moderation would need to be in place too. Preferably on a per-category basis, so your reviews might have "good karma" on some topics and "bad karma" on others.
The 5-star McDonalds may be a really good McDonalds that's very clean and consistent, but the $50/meal ocean-side bar only has 3-stars because the steak is sometimes rare instead of medium-rare. People are rating relative to their expectations of the restaurant, so someone who doesn't share those same expectations will be confused that a dollar cheese burger is 5 stars but a prime rib steak is 3 stars.