TRIVIA Answer :
When may amateur radio operators use their stations to notify other amateurs of the availability of equipment for sale or trade?
A. Never
B. During Ham Swap nets only
C. When the equipment is normally used in an amateur station and such activity is not conducted on a regular basis
D. When the equipment is not the personal property of either the station licensee or the control operator or their close relatives

Answer C is Correct!

Some amateur radio operators feel that buying and selling ham radio equipment must take place during ham swap nets, FCC part 97 is very clear that it can be done at any time as long as it's not on a regular basis.

The current Technician Class License Question Pool does include this topic.
Q. When may you use your station to tell people about equipment you have for sale?
A: When you are offering amateur radio equipment for sale or trade on an occasional basis

Amateur operators may, however, notify other amateur operators of the availability for sale or trade of apparatus normally used in an amateur station, provided that such activity is not conducted on a regular basis;

More on part 97 Station Operation Standards