I remain unconvinced.
I wasn't actually recommending that someone should sell 10 cheap basses a year, certainly not you in particular.
As you say, you very rarely buy/sell basses. That puts you at one end of the curve, the end where signing up to the Market to sell a single affordable bass makes very little sense. I wouldn't try to argue it any other way.
Me, I'm at the other end of the curve. I'm forever buying & selling basses, amps, pedals, whatever. That's not some sort of 'value statement', merely an observation. For me, the Market fee is therefore negligible, maybe 50p per item.
Your final point just doesn't work for me. A small, almost nominal, fee will very probably cause a narrow range of affordable basses to become marginal propositions, or at least more marginal than they were before. It certainly will NOT cause the withdrawal of £300 basses in favour of £5000 instruments.
I think a lot of Basschatters are under the impression that Basschat is now a huge concern, with thousands of enthusiastic members who are potential buyers of their basses. The various statistics in the public domain do tend to give that impression.
BUT
Actually spending time on Basschat, seeing who is posting what and where, gives a very different flavour as far as I'm concerned. I suspect that there are no more than a few hundred truly [i][b]active [/b][/i]Members and a helluva lot of dormant user names.
If you think you're reaching a potential market of many thousands of active bass players with money in their pocket, then prepare to be disappointed.