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Well for some stuff you are right, its complete junk but I leave stuff on eBay for ages sometimes.
I have some items up at the moment and I dont expect some stuff is exactly in high demand, its a limited market of collectors out there but where else is someone going to find a vintage lens cap for a Sigma in 65mm size. Someone out there will be restoring te lens and hoping they can find an original cap.
Some stuff maybe wont ever sell and that definitely applies to broken electro flashes but I would pay happily for a mint Agfa bulb flash and some bulbs and I would pay at least £15 for a Tamron lens cap, old style logo in 67mm size for a vintage lens I have. There may well be someone out there who badly needs an old SunPak flash
who knows it may have bits inside at allow a stranded time traveller to construct a time machine to get home.