From ebay's perspective, large traders mean faster dispatching and better refunds/disputes.

With a guy selling out of his garage and a seller who says they didn't get the item, you don't know if the item was mailed (or even ever existed), and they'll probably kick up a stink if you make them eat the cost of items lost in the post.

Easier to have traders you can form trust relationships with, and who have deep enough pockets to provide a good return/refund experience.

One thing eBay seems to be doing better at than Amazon, is having well known retailers using them as an outlet. I also find it amazing how PayPal has morphed from a payment option that people may have used on suspect e-commerce websites, to something that is expected when customers check-out at a major retailer.

They have been taking active steps to partner with retailers, their relationships seem to sour quickly, at least in the case of Neiman Marcus. The partnership was abruptly shut down because Neiman Marcus said, "It did not meet all our expectations." Hope eBay can set appropriate expectations.

eBay works with most major retailers out there ( like: http://www.ebayenterprise.com/news_events/news_releases/gsi_... is still going strong). I have no idea what happened in the Neiman case, but it definitely seems like the exception, not the rule.