Provide quality items at good prices.

Do you get a lot of repeat buyers? And why would you block a buyer who left you positive feedback? What ratings do you reckon they left you? Given the frequency of your recent feedback it shouldn't be too hard to work out who it was. If you're that worried, presumably you check your stars frequently. Which, by the way, aren't at a catastrophically low level.

The low DSRs will drop off in 12 months anyway.