As of May 2019, this service is no longer available.
eBay made changes where it's no longer possible to figure out winning bidder using below method.
Find User ID of eBay buyer who won given auction
It used to be very easy to get the User Id of buyer who won eBay auction. You could just look at bid history page and you would get full buyer id.
For the last several years, eBay has been on a mission to make getting that information more and more difficult.
Up to the end of 2013, even though it was already more difficult to figure out buyer id because eBay was showing incomplete user names that looked like this: e***3 ( 1228 ), you could still figure out full user name by looking at the feedback.
Towards the end of 2013, eBay made a change that made it impossible to do it that way.
How to find out eBay Bidder ID?
Currently, there is still a way to sometimes get full user name of a buyer who won given auction but it's not as easy as before.
This service was created to try to figure out full eBay bidder id of user who won given item.
You need to provide eBay Auction Number and it will tell you if full buyer user name can be extracted.
If full user id can be extracted and you would like to know it, this service will cost you $9.95.
In case full User Id cannot be retrieved or if the method being used stops working, you'll receive a refund.
It should work with any eBay Global Site including US, UK, CA, DE, AU.
Most of the time you will not be able to get full user name right after auction ends.
It's best to wait for an auction to age for at least a few days. The best time to try is between 1 and 3 weeks after the auction ended.