Thanks for all the great advice all! It is a bit disheartening when you know you've done the best you can and still you get gyped,

You didn't get gyped, the buyer left you positive feedback did they not? 

I would worry more about blocking buyers who don't pay than buyers who leave a 4 in your DSRs. As far as I know you can only put non payers on your block list

Seriously, coming from the view point of a buyer I don't even look at the DSRs when I buy, I only look at the feedback.

I think you're being a little obsessive...