is this allowed?

[13boeder]

" 

If you don’t remove your inappropriate feedback I have know (sic) choice than to also send you a negative feedback and see how it feels to overreact unnecessary is totally inappropriate"

I got this from a non-seller (auction ended, they cancelled the sale without warning, apologised for that policy breach, then relisted the item at a much higher price) for whom I left polite but negative feedback.

Is there anyting I can or should do to prevent this?

[plpmr]

 As you also sell on this account - block them.

They cannot leave bad feedback for you as a buyer - if they leave a bad comment on a green dot you can report to eBay and they will remove it. 

[13boeder]

Thanks. I blocked them as soon as they cancelled the sale.. I wish that also stopped the emails....