Question is: Why now?
eBay survived Panda updates for years with the same crappy content. Is this Google's reply to eBay's recent changes on their Adwords campaign?
– Panda 4.0: Why eBay Just Lost 80% of its Organic Rankings
"By knocking eBay's product listings pages out of the organic rankings, Google is forcing eBay to use product ads to stay in front of those searchers seeking information about specific types of products.
It would be easy to say that profit is the sole motive here, but this is actually good for users too. eBay’s “strategy” of pushing out millions of doorway and internal site search pages was spam by anyone’s definition. For commercial queries, Google shopping ads offer the most useful customer experience."
Panda 4.0, Payday Loan 2.0 & eBay's Very Bad Day
"Over the course of about three days, eBay fell from #6 in our Big 10 to #25. Change is the norm for Google's SERPs, but this particular change is clearly out of place, historically speaking. eBay has been #6 in our Big 10 since March 1st, and prior to that primarily competed with Twitter.com for either the #6 or #7 place. The drop to #25 is very large. Overall, eBay has gone from right at 1% of the URLs in our data set down to 0.28%, dropping more than two-thirds of the ranking real-estate they previously held.
It is entirely possible that this is temporary, and it's not my intention to "out" eBay – I have no idea if they've done anything that merits major ranking changes. This could be a technical issue or a mistake on Google's part. It's also worth noting that these results only track the main eBay sub-domain (www.ebay.com), not other ranking sub-domains, including popular.ebay.com."