ebay accounts are to be anonymous except for email address when requested, or square trade verifying or PayPal.... But, one would have to know the item listing to this particular item being auctioned, and time frame for ebay search to find a record of it, in 6 mos they are no longer linkable if you bookmarked the item? Someone gave them their ebay account info or was subpeona?
Sort of, once you have bid on an item, either bidder or seller can request the contact information of the other.
Closed listings remain available to general search for only 2 weeks. If you have the listing number, it is available for 3 months, but I have seen listings that remain a fourth month due to vagaries in the system. I doubt they had to subpoena the ebay records, ebay's policy is to cooperate fully with all LE investigations. It would be a natural place to look for leads, not to mention help account for any missing personal items, just in case Scott claimed that items were stolen, when in fact Laci sold them.