Here's my impression, for what it's worth.
I would be very upset too if someone sent an item to me with a sticky note saying it only worked in limited circumstances when that was not mentioned in the ad.
I expect an ad to have all the details & it is very unfair on a buyer when faults aren't mentioned.
I was in a somewhat similar position once when I bought a table. Asked questions, then when it was delivered it had white marks on tabletop that had not been visible in photos OR mentioned when I asked questions. Seller response? Oh yes it could do with a repolish. That wasn't what the ad said-ad said excellent condition.
So I get it, I know exactly how you feel.
I am glad you won the case and if the seller isn't prepared to pay for return postage, too bad. If they ask again, just reply you are happy to return the item but not at your expense, they need to provide a bag or label. And follow through. If they do send the postage, be fair and post it back.
But if they won't then don't.
Apart from that, I wouldn't be getting into any further discussion or dealings with them.
I don't think you necessarily handled anything wrong. I would also take offence if a seller told me they would refund for a faulty item but only if I said sorry. That is unprofessional and has nothing to do with whether the item was faulty or not. They brought their troubles on themselves. I don't care if they have sold 6 things or 6000, if an item was faulty and they knew it, they should have just bitten the bullet and offered a full refund with return of the item or a partial refund & you kept it- and be done with it.
