This was a good call. eBay has just officially denied that the user data is theirs [1], and there are claims online that the data was from a separate previous breach [2]. This is almost definitely a scam.

[1] http://www.digitalnewsasia.com/security/ebay-hackers-offer-d...

[2] http://www.reddit.com/r/netsec/comments/267015/ebay_user_dat...