Never respond to a seller's threats that they will leave a negative for you as a buyer, this is against eBay's rules and policy, as you can see there is no red negative facility to leave negatives for buyers.
You have received one, is this from the same seller ? Contact eBay Customer Services, and report it, they will remove it, and place a policy restriction on that seller's account.
This is the easiest and quickest way to contact eBay Customer Services, for a Call Back option.
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid
Lines open 8 a.m. - 10 p.m. on weekdays
9 a.m. - 6 p.m. on weekends.
Automated agents will be available on chat outside of the above hours.
I recommend contacting CS first thing in the morning as there's more chance of Dublin answering.
@uk-lucil