It's strange isn't it. I post things I sell on eBay all the time, mostly signed for and they never get lost. One was never collected from the post office and returned to me, but never lost in 10 years of eBaying.
The random low cost things I send just standard Royal Mail no signature, same packaging always get lost and the buyer needs a convenient refund
I buy loads of eBay I can't think of anything I've not received. I think one thing was resent from a business seller.