A few people in the past have posted things for sale. As long as it is not commercial in nature and the item is related to home automation, I don't really see a problem with this. ADI would obviously have any final say in the use of their forum for this. To avoid becoming an auction site, always put an asking price and leave contact information so that anyone interested can contact you directly. Also, come back and edit the post to indicate when something is sold. You could list the items in the "General HA" section.
"If you don't know what you're doing, do it neatly..."