I was once a moderator on a forum and we had an approval process for for sale threads. They were not visible until we went on and said yes to them.
Helped us out no end cos we were always getting this problem
I'm not sure that we have that capability.
It's worth a go if you have. People (mainly noobs) sometimes got pissed off waiting longer than 30 mins with it but our response was always "This forum is free, you don't pay anything to list stuff here. If you don't like it, tough tits"