Personally I think the ability to block buyers is part of my right as a seller.
Pre internet/ebay days, when everything was done through mailorder or in person, I could "block" a person by:
-no longer sending my pricelists to them
-telling them I couldn't help them anymore (ie return the uncashed cheque etc)
-if in a B&M ban them (I've never had a B&M but I know fellow B&M storeowners who banned buyers from their store, and for good reason)
The reasons I block buyers online are based on risk and cost:
-items lost to a location
-too much work/time/cost to sell an item (lots of questions, issues before or after etc)
-unreasonable demands or issues with the transaction
Certainly I'm sure some folks over-react but I am glad to have the ability to block buyers.
With respect to the main topic, I have "caught" bad blocked buyers purchasing from me via new id's over the course of years (ie they come back once or so each year with a new id, name etc). I have ways of being able to catch this.
In the situations where I called eBay for help, the CSRs were very helpful and generally (see 2nd aside below) fixed the problem for me with no defects or whatever was the risk at that time. I do know that they were aware of the linkage between the ids and the problems.
As extra asides:
-in one case I realized that perhaps whilst I blamed the buyer for the issues, it was quite possible that it was someone in the postal system that knew what stuff was safe to steal from that particular buyer. I will never know.
-in another case, when the bad buyer came back and purchased another $500 item the ebay CSR and PAYPAL wanted me to go ahead and ship again. I really thought that was stupid, but I sent it in a way that I was covered (this was a failed transaction covered by PAYPAL kind of loss) and darned if it didn't go through ok!!!
