That's the challenge to write a program to associate masked id's with real id's. The two characters in the masked ID are randomly chosen from your real eBay id. Although it doesn't say so specifically, the feedback rating does seem to come from the actual bidder.

Here's the info I received from eBay regarding the change:

In order to protect our community members from threats such as fake
Second Chance Offers, we have changed how bidders' user IDs are
displayed on the Bid History and Item Listing pages on eBay. eBay limits
how your bid history information is displayed by using masked user IDs,
so that other members cannot view your member-specific information --
such as your user ID -- on the Bid History page. Your masked user ID is
based on a combination of two random characters from the actual user ID
and three asterisks in the middle, e.g. x***y.

Regardless of the current high bid, masked user IDs will appear
throughout the duration of the auction. Masked user IDs may also appear
more than once in the bid history and may represent different bidders
from different auctions.

We believe that this change will help to balance the need for openness
and transparency in the marketplace with the need to protect our
community.

As part of this initiative, we also added additional bidder-specific
statistics to provide the community with enough information about the
bidders involved in a listing for them to feel confident in placing a
bid. You'll see this additional information on listings where the user
IDs of the bidders are masked.