luckyduck, I can’t pass a charity shop without popping in. Always have a rummage, as does my wife. It is a numbers thing, we reckon 1 in 20 to strike lucky - the down side is we have 2000+ books and more pond yachts than I’ll ever use.
As for FB Marketplace I have several search terms and leave the FB algorithm to do its thing.
I have noticed that pond yachts and r/c boats that need work or restoration don’t sell on FB. The Marblehead was listed for £180 - probably a bit ambitious but a fair price if no work was needed, I bought it for £50 as no one was interested. It just needs some cosmetic work but could be sailed now.