If I were a customer, it would be a simple issue, as "review" sites are very common. But it's definitely crossing a hazy line to do the same as a "competitor". Though I kind of like the watchdog idea. Given that there's no regulation in our field, it almost seems like a very needed thing.
I've been good about not getting dragged into the whole flame war thing, though recently he emailed me pretending to be someone else wanting to buy my company and I could either "sell or be crushed". I did write back a few times on that one with a bit of humor, having fun with it. But after a while, it's just lost it's humor, winding more into creepy stalker territory.
I'm fortunate in that he's left a trail of emails and voicemail behind him that demonstrate the situation for what it is, but it just feels plain awkward, like it shouldn't exist in the first place.