Is abusing rich snippets markup against Google’s guidelines? Yes, according to one Google employee, abusing rich snippets is a negative signal, and a penalty is possible if caught (either manually or algorithmically).
Q: “Even though Google offers no Rich Snippets for category pages, I regularly encounter such results containing Rich Snippets for listing and category pages, due to malicious market. Most of these go against your guidelines, but end up generating Rich Snippets nonetheless, often forcing competitors to do the same thing. Are there any plans to step up countermeasures to discourage the publishing of such malicious markup”?
A: “… if somebody combines this [local business] markup with actual product markup. So, if they have a product on a page and then they add the review, and instead of the actual product review they add this review aggregate from the company, then immediately it would be definitely a clear violation of our guidelines, and that’s something we would definitely take action off. I’ve seen a lot of spam reports, and in my experience, we definitely – whenever it’s clearly a violation -, we definitely take action” source