I want to let users post classified ads on my forum.
There would be two categories: buy and sell.
I would like to put these two categories, which are very related, in a parent category called classified ads. Obviously, my users should not be able to post in the classifieds classified ads category as it exists only to put buy and sell together.
The only way I see to do that it to prevent my users to post in classified ads but the thing is that they will still be able to display the content of the classified ads with “no subcategory”. The classified ads category will never contain any message so it’s weird to let my users see this page, they won’t understand why it is empty (I could add a message on this page, but that’s still weird). Plus the classified ads category will display a number of 0 message in the categories selector (as this selector displays only the number of messages from the parent category without subcategories).
Maybe buy and sell could simply have no parent category, but this is a bit weird as these two categories are completely related. Plus, I may want to add a third category (hire/service)? That would be 3 categories very related to each other and with no parent, although classified ads are not the main part of my niche sports forum.
Also I don’t want to use tags on my forum for various reasons.
So I’m not sure how to organize these categories.
What would you do?