Not circumstantial evidence as loose as what you just described related to shilling.
I think eBay errs on the side of what makes them most profitable, and that means no, I don't think they do a good job. I've spent a few hundred hours over the last decade trying to get eBay to get rid of some specific scammers, and all I can really say is that if you give them solid proof, they usually act--but far more often than not, there is little or no definitive proof that's possible to get. And I also believe few people understand what "solid" proof is and just think if they report someone, that should be the end of it. Most people expect eBay to act as legal and ethical enforcement, but the main problem is that eBay has few ways of gathering evidence if the person doing the reporting doesn't give it to them. I wouldn't be surprised if they periodically and/or sporadically fail at acting upon solid proof given the volume of scammers they deal with, and yea, they deserve to get hammered each and every time they do that.
There have also been several threads started on the Ebay comic board about this auction, and all of them have been pulled. I guess I assumed they reviewed those threads before pulling them
Usually the only threads I find on ebay are about scammers like this or people on a rant about why graded comics are bad.