It seems Yelp is now labeling reviews on business profiles that they think have fraudulent and paid for reviews.
The Local Search Forums notes some business profiles showing the warning.
The warning hides the reviews on the profile with a "Consumer Alert" box. The box then reads:
We caught someone red-handed trying to pay someone to write, change, or remove a review for this business. We weren’t fooled, but wanted you to know because these actions not only hurt consumers, but also honest businesses who play by the rules. Check out the evidence here.
You can then click on the "Show me the reviews" button to see them.
There is a link to click on the show evidence which Yelp will share a screen shot of the evidence and one shared such an example in the thread:
That is pretty transparent and it would be cool if Google went as far as to show you detailed examples of when you break their guidelines.
The mobile version doesn't have a link to show the reviews, it just takes you to the evidence.
Forum discussion at Local Search Forums.
