Boy, I can relate to this. It's so hard to let it go sometimes.
There was a guy a couple years back that for whatever reason, decided he was going to start a negative post about a product of mine on the #1 forum for the niche. He didn't even buy it new... He got it at a garage sale. He had no idea what he was talking about, and luckily people who are good customers of mine backed me up and made him look stupid in the end. But like always... A couple negative types piled on in the thread. What bothered me the most is that the first guy took all these terrible photos showing the inside guts of our product, which 1. Makes it look like crap. And 2. Shows the whole world how it works. One of the negative guys that piled on has since been going around using that post as a reference to tell people they should make their own. I already confronted him about it once, and just basically asked him: "What exactly do you have against me?" He of course played stupid and acted like he didn't realize he was focusing on me. Since then, I've found three other forums where he's done it. Just found another one yesterday when I checked a back link in the logs. It's like he has some bizarre obsession with trying to talk people out of buying our stuff. He's never even bought anything from us... I don't know him from Adam. It's just weird.
And the best part is... When you search on the product name, the negative post comes up #3.
It's one of those things that probably doesn't do all that much damage overall, but it just bugs the hell out of you. Then on the other hand... The idiot does post a link to our site after all. It would be great to know if any sales actually come from that. That would make me feel better. lol