Post a picture with your ad. You'll need a URL to post a picture. This can be the location of the picture at your own site or from any other site, such as an album on a photo-sharing site. Then, each time your ad is accessed, the picture will come up with it. If you want to post several pictures, either gang them together and scan them as one photo, or post one with your ad and give URLs to the others in the body text of your ad.
Many good deals are to be had from dealers who have taken good previously-owned equipment in trade.
And many dealers offer a warranty on used equipment. Here's what to put in your ad so it will attract attention and readers can respond to it quickly. Manufacturer and model. Type of equipment, Scanner, Digicam, Printer, etc. Description and any extras that are included.