While it looks like you recognize the irrationality of posting bogus reviews for your competitor's product, buying some Adwords for "[their product name] reviews" and "[their product name] alternative" is worth looking into. Of course check out the search trends and the PPC numbers to see if it makes sense, but it just might. If they're on Twitter, get a few tweets sponsored targeting their followers. A bit underhanded, but totally legit, and not an uncommon practice (and will help satisfy your thirst for revenge). Anywhere else you can find their customers, make sure you're there, highlighting what makes you the clearly better alternative. If your product truly is more valuable then you're not stealing their customers, you're rescuing them.