Haven't read through the whole thread, but thought I'd add my views.
I think £7 one off or £20 yearly fee is reasonable if you are selling regularly or selling a high priced item.
However, for someone like me who won't be selling much, I think it is pricey.
I have a fretless P bass to sell now, I'm only looking at selling it for about £120. I'm loathed to pay a £7 fee as I worry it wouldn't sell and that is a big percentage of the sale cost (not flashy enough for many basschatters and quite a specialist item), however, I can list it on Facebook for free and can wait for a free listing day on eBay and only have to pay fees if I do sell it.
(Note, I'm not trying to advertise my fretless here through the backdoor! However, if someone read my post and did want it I would pay a £7 out of politeness )
So whereas Basschat would have been my first port of call previously, now I am put off by the fees in view of my comparatively cheap items!!