The location of the original auction was listed as Camden, so I would think it likely that the original owner ended the auction early and took the bass to the Gallery for them to sell on commission. In my experience they ask how much you want to sell for and use that as the asking price before suggesting a valuation.
It looks like a lot of work has gone into the carving, but I think it would need a more upmarket neck & tuners rather than the chinese squier affinity bits to be seen as a £900 instrument even for someone who is into dressing up as a pirate when they play - if anyone like that exists.