I think you have gone above and beyond and your email is very restrained, polite and informative.

They may very well neg you but if they are as toxic as they appear it will probably be extremely rude with capitals so will make them look like the flaky ones, especially if you follow up with a reasoned, polite response.

I never let the thought of feedback influence my decision when it comes to problem transactions, no way would I do other than what I consider right just to try and influence a buyer's choice of colour for feedback.