Q) When may amateur radio operators use their stations to notify other amateurs of the availability of equipment for sale or trade?
A) When the equipment is normally used in an amateur station and such activity is not conducted on a regular basis.
It is common to hear a "swap-and-shop" during the regular course of an amateur radio net. These can be a great way to pickup amateur radio related gear. Local nets offer the additional benefit of being able to pickup the item locally and talk to the ham before the purchase.