The yellow banner has a little box at the right side, like other system notifications, that will dismiss/disable it.
I don't know if that is thread-specific or a general preference setting.
goto your classified "For Sale" posting,
in the top right corner, click the drop down menu button labelled "Administrative"
The radio button "Close Thread" should already be selected
This administrative menu only appears on for sale threads that you have started.
Another forum I participate on only lets you post the ad, edit the original and close the ad - no bumping allowed, all discussions are to be done via PM's. I too don't like the over bumping.
Also, maybe we should have another sub section for 'ConUS only' sales....... hat, coat, I'm outta 'ere....
I've attached a screenshot of one of my classified postings for reference. The administrative button is right there next to the thread tools button...and, yeah, I see that the administrative button is missing on your screen shot.