We have an amusing chicken and egg situation here...
a) I hadn't considered that people are so respectful of the list, and don't want to offend, that they don't post their "for sale" messages. (THANK YOU ALL FOR BEING RESPECTFUL! You're doing a great job!)
b) But, since no one's posting, despite the guidance of these messages to post in the "Installing and Using OpenWrt" category, no one sees anyone else posting, so they keep their head down, and don't post.
I'll restate my reluctance to create new categories: they make a hassle (not for admins - it's two minutes work), but for every person who wants to post a message.
Every time you want to post, you have to decide (or guess) where to post a message. If you post to one category, some people (who never read that category), are never going to see it, even it if might have been interesting... So it provides friction for people who want to post, since they're not sure where it best belongs.
So - I still say, "Post away!" Post in the "Installing and Using OpenWrt" thread. If we get people complaining that we have too many "for sale" posts, we can revisit this discussion.