Cleaning up my eBay watch list

It's time to clean up my eBay watched items list again, so I thought I'd make a note of some of the high / low prices people paid for items:

• Canon EF 800 mm IS f/5.6 L Lens failed to sell for £3400 - this lens retails for about £10,000 new! They're not often on eBay, but I think around £5000 - £6000 is probably more the going 2nd hand price. I actually really wanted to buy this lens as it is such a good deal. But I can't really justify spending that much money on a lens I wouldn't be using constantly. It was later relisted and sold for £2,900! Condition was only used a couple of times for testing and warranty not registered. (Though I think you would need a retail receipt for the warranty, so that probably doesn't make any difference). No feedback has been left for the seller for this transaction though, so it's not possible to say if this was a real deal or not.
• Samyang 14mm f2.8 ED AS IF UMC Lens - CANON EF Fit with Filter Holder - Boxed sold for £202 - not a stunning deal, but pretty good. The lens by itself normally sells for around £200-250 2nd hand.
• A Canon FD 800mm f5.6 lens sold for £685.66. I guess that's a good price for a 800mm lens, even if it is manual focus.
• DE OUDE DELFT HOLLAND LENS Objektiv RAYXAR E65/1.0 sold for £27.85
• DE OUDE DELFT HOLLAND LENS Objektiv RAYXAR E50/0,75 sold for £83.94
• DE OUDE DELFT HOLLAND LENS Objektiv RAYXAR E65/0,75 sold for £63.54 (but was then relisted, so presumably the high bidder didn't pay. The second time it sold for £78.45.) As far as I'm aware there's no way to get 'usable' results with any of these lenses on a digital camera as they need to be positioned too close to the sensor.
• Samyang 14mm f2.8 ED AS IF UMC Lens - CANON EF Fit Boxed but no lens cap sold for £149. That's at least £50 under the normal price, maybe the lens cap costs £50? Or maybe bidders were put off by it having no lens cap, but the seller claiming it had only been used a couple of times. How could they have lost the lens cap with that amount of usage?
• CANON EF 50mm f1.0 50 1.0 with HOOD in VERY GOOD CONDITION was sold for £2,051. However, the buyer later left feedback saying Never received! Made some excuse up about breaking it!! No evidence, AVOID!!!!
• A Novoflex Castbal T-S Tilt & Shift Bellows with rail, right-angle bracket, and Nikon attachments sold for £225. This was Mint condition with original boxes and When bought as new... would cost well over £400.
• Canon EF 600mm f/4L IS II USM Lens Super telephoto sold for £5,577.35, that's right, nearly twice as much as the 800mm IS lens sold for.
• Novoflex 35mm/3.5 Noflexar Weitwinkel für Exa/Exakta sold for £44.72. Condition was D = Gebraucht und funktionsfähig. Die Linsen sind sauber, alle Ringe laufen, stark abgegriffen. (that's D = Used and functional. The lenses are clean, run all the rings, heavily worn.. It looks okay in the pictures, so I'm not sure what the problem was with the condition.
• A different copy of the Noflexar 35mm f/3.5 sold for £65.11. Yet a copy that had issues with the optics (soft images when viewed at 100%) sold for £77. Normally this lens sells for around £100.
• Canon soft focus 135mm lens hardly used (but looks like no box) sold for £81. That's pretty good for this lens, usually £100 - £150. Another lens I would really like but can't justify spending that much money on given how much I'd use it.
• Lensbaby Soft Focus Optic sold for £22. I wish I'd bid on that now. There was also another seller offering a few new ones for about £30 BIN. But I checked a few weeks ago and they'd now sold all their stock. :( Another one that was missing some of the aperture rings sold for £18 (BIN).
• tomodachi life Nintendo 3DS New and sealed sold for £31.50 despite only being £25 on Amazon at the time.
• An unusual item - CANON EF 400/2.8 L USM II mit ORIGINAL Madonna Signatur sold for £2,008.30
• Olympus OM Zuiko 18mm f3.5 sold for £485.15. That's not a really high or low price compared to the normal selling price. But it still seems a lot compared to similar modern lenses to me.
• NiSi GND8 100x150mm Square Reverse Nano Graduated Neutral Density Filter -MARKED sold for £9.50. This seems pretty good to me. The filter did have a scratch, but reverse split ND filters are pretty expensive.
• Very Rare Kuribayashi K.C Petri Orrikor 35mm f/3.5 lens - UV Transmission sold for £53