I was totally confused about this ad issue. Those ads violated Google's/YouTube's advertising ToS (Terms of Service) in every possible way.
After doing some sleuthing, my only guess was that eBay's ad department had tried to skinny past YouTube's rules for some nutty reason. (They may still be behind this nuttiness! I do not know!)
When it went on for a number of weeks, I finally sent Google/YouTube a letter, with screenshots and a query, in regard to their advertising ToS and those dang ads.
Here are the specific violations of Google's/YouTube's advertising TOS that I wanted to know about (and they are surprisingly strict!) in this case:
One The eBay ads were completely opaque— YouTube doesn't allow ads that aren't in some way see-through.
Two The eBay ads were not removable— YouTube insists that all banner ads be visibly removable.
Three The eBay ads were in a physical place on the screen that YouTube doesn't allow for Banner Ads. Especially the opaque ones. That you cannot remove.
Soon after I posted that letter, the ads disappeared. Could be coincidental. Could be that a bunch of people sent letters. Could be someone actually read it. I don't know.
The only fact I know for sure is that I now have an irrational dislike of all things eBay and an unexplainable twitch in my eye when I see anything on the web tinted "Egyptian Blue."