Of course I agree it's so disappointing if a buyer leaves a bad feedback before trying to resolve a matter with the seller, some see the feedback option as a messaging board.
Thankfully, they left this on a neutral so it doesn't affect your seller performance.
Have you tried to work this out with the buyer, then you can send them a feedback revision to complete.
If you think this neutral is affecting your sales leave a follow up, but be aware to be polite and factual, as potential buyers will read feedback from you and can see how you deal with problematic buyers.
@antsattic-85b