It is not uncommon on forums to be called out when you say something rude or derogatory to an upstanding member. Whether you were talking to Verbster or MovingConcierge doesn't matter. I couldn't believe you would take such offense to your own customer just because he mentioned that traffic or referrals (or whatever) had died down at your site. Site exposure is obviously the point of buying a link on your site. Do you think a buyer has a right to post that traffic and/or referrals have died down?
You may have been dealing with some life issues that were stressing you out, but belittling your own investors is just bad business. You have after all made transactions with them. They could easily ruin your trader-rating here (and therefore your reputation as a seller). It's easy enough to send a PM to someone if you think he has wronged you or your business by making an unwarranted post.
Namepros is one of the most active forums on the net. You mentioned you weren't trying to make enemies here... so don't. If you make enemies at Namepros, it will most likely carry over to other large forums and definitely carry over to other domainer forums.