The OP's seller is doing us all a disservice big time.

eBay had this problem in the US some years ago.

They fixed it by simply extending FVF's to postage price as well.

Problem solved!

But sellers who sell low value high postage items were severely impacted.

The OP has done the right thing by reporting this scammer.

Noone likes FVF's and they are high but the alternatives are a lot worse.