Feedback does not mean much considering you
screwed this buyer out of something they entered
into a contract to paid for. They do have a
binding contract with you and if desired they
could take you to small claims court. 

If you were really concerned about the "rumors"
you should've asked for their number and call them
to discuss the matter. I doubt you did and it is
true you did not have to do this. But at the same
time the quick turn around time in which you sold
the cel to someone else is HIGHLY SUSPICIOUS.

And assuming the buyer did contact you regularly
via email, your claim about them not communicating
with you is pure lies. As a seller, regardless of
your feedback history... your conduct in this
specific auction is highly unprofessional and
questionable. 

Lastly, I could careless if someone has 1000+
positives but has some negatives, that is what I
care about. How did the user conduct themselves to
earn the negatives? IMO each auction is separate
unto itself and that means, each auctions feedback
is EARNED. It doesn't matter how many positives
you had in the past, what matters is the PRESENT
for my specific transaction with you.