Buyer bought a new in packaging collectable from me, received it opened it and said it didn't work.

I paid for return postage and when I received and tested the item it worked fine.

Buyer still wanted a refund.

I checked and the buyer also did this to another seller (we exchanged messages) for a nearly same item on the same day they bought mine.

That makes 2 sellers that now have desirable collectable items that were in original packaging now virtually worthless as they have been opened.
We have both had to pay return postage so are also out of pocket for that.