You used to be able to block users with a negative feedback score (minus 1 or lower) but that was pretty useless, a vestige of when sellers could leave negative feedback for buyers (which they haven't been able to do since 2008) and it was removed fairly recently. There never was any such block for anyone with 0 or higher.
You can LIMIT the number of items anyone can buy from you in a 10 day period (being lead bidder in an active auction of yours counts, and this can prevent a rebid in that auction) and then exempt those with more than x (maximum of 5) feedback score (the language eBay uses is block those with x or less but that confuses many who think it is an outright block rather than modifying who the limit applies to, who then come here and insist that they blocked such low feedback users but it didn't work because one bid on one auction of theirs). Note that the lowest you can set the 10 day limit is to 1 item so it does not block anyone from bidding/buying/offering on the first item.
https://offer.ebay.com/ws/eBayISAPI.dll?BuyerBlockPreferences
