The negative won't harm you as much as the policy violation will. NEVER leave feedback like that... apart from being a breach of eBay policy (which can get you restricted), it also makes you look like a goose.:^O:^O

And has just increased this buyers green dots and stars!

OP, when buyer refused cancellation, why did you not open NPB instead of sending rude messages? Once the case is closed I don't think either party can leave fb ?