as tressygirl has pointed out, when buyers arrange for collection by their own courier collection they disqualify the transaction from eBay’s money back guarantee. This was introduced precisely because some buyers were claiming a refund from their seller when their own courier had damaged their item.
The only point of caution is that, if the buyer paid eBay by credit or debit card, they may still be able to claim through their card issuer. This is beyond anyone's control, even eBay.
The fact is that there is no entirely safe way to sell (or buy) through eBay. It's up to the seller or buyer to judge for themselves whether the risks are worth taking. You may, as you say, risk bad feedback and even an account defect for refusing to complete the sale, but this no longer includes a "fine".