Thanks for the advice guys, I really appreciate it. I'll definitely do all of the checks mentioned above, and thanks wheelers for some good tips!
I get that it's a lot of money to spend on a bike without a test ride. I'll definitely want to see it running (and will ask to see a cold start as Wes suggested) and will either ask for a quick pillion ride or to see him ride it round the streets. I'll at least be able to hear the gear changes that way.
I originally found the bike for sale on a forum for that specific bike. I've been through all of his post history and can see that he's fixed some of the electronics already in the past and took it in for a recall.
It's the bike I've dreamed of owning for years, and been saving up for it relentlessly. I haven't seen one up for sale in a very long time! Its a 2012 BMW S1000RR in the rare blue fire colour It looks like it's been meticulously cared for.