If you don't wish to sell to certain eBay members, you can put them on your blocked list. Members on that list will be unable to bid on any of your listings until you remove them from the list. You can block up to 5000 User IDs.
To block a member, enter the member's user ID and click Submit. Separate user IDs with a comma.
To remove members from the blocked list, select the members' user ids and delete them. Remember to inform the members so they can resume bidding on your items.
You can restore a past blocked bidder/buyer list by clicking on Restore list. Remember, you can only restore blocked bidder/buyer lists from 3 months prior to today, inform the members so they can resume bidding on your items.