Back in January I suggested a caption be added to the photos (Thread; Photos Caption) and am still hopeful that it will be taken-up next time there is a major site update. Also I've noticed in the past that minor improvements will suddenly appear without fanfare if they don't need a lot of re-design to the basic lay-out.
So I'm still hopeful that a caption will be added at some stage. In the meantime I do add a "Click on photos to enlarge" line to my description. (when I remember )
My reply to the idea that ebid's thumbnails are too small to be useful to make an informed buying decision would be this. How often do I see complaints on that other site that buyers all too frequently buy after only looking at the photos and not reading the description? Then start a return.
On ebid I've never had a return request, my one and only return on obay was for exactly this reason. A chipped item, had the buyer looked at all the photos (instead of just the thumbnail) or read the description, both of which clearly illustrated the damage, they would not have bought the item.