[petra]

The problem with reddit is that the comments there could also be ads, and it's harder to tell.

[noogle]

Ranking results by author's credibility (site karma) could help, at least for the time being.

It's not that the comments are plain ads (these will be easy for the reader to discern), it's dishonest product reviews. It's an unsolved problem in e-commerce websites and even in real life.