Whenever anybody unfairly trashes my stars, I immediately add them to my BBL and block them, then I leave a follow-up to their feedback which essentially names and shames them.

Example: [UserID] scored low postage DSRs despite receiving item in only 2 days. Sellers beware.

You don't have to leave them feedback if you don't want to, but if you do, you can say something similar, but don't make it sound too much like a negative comment or eBay might remove it. Something like "Prompt payment but why did you unfairly trash my DSRs?" should be OK. Might make them think twice before doing it to somebody else.