Not being funny, but I'm not sure I'd buy a 3 year old Model S off you matey, not if you've only spent £60 on maintenance and that was only to get the mechanic pissed ;-) (£20 for a pint down your gaff? crickes!)
I'd never buy a car without a service history from the manufacturer (especially <3 year old); it simply states that the owner cared enough for the car to make sure that those with the relevant expertise have looked after it. This is an EV, that relevant expertise is (currently) hard to find outside the manufacturer (I wouldn't let my usual workshop look at it let alone service it). As (if?) EV ownerships grows significantly, then back-street garages may very well take the time and expense to train their staff in EV servicing, but I don't know of any in my area with that expertise. Changing the brake pads and wipers could be done by a trainee at any garage, but that's not a service.
All that said, £450 a pop does seem a bit steep, it was only £300 on my Seat Leon ;-)