I bought bikes unseen, to be honest not a good idea even if coming from an Em!, Truthful dealership, wont make that mistake again.
Best go see the bikes, best plan on a weekend with 2-3 bikes to go see, close to same areas, do not decide then and there, unless very sure it's what you want.
It is a lot of money to lash out on something previously owned by a stranger, I get that, but sometimes you just have to take a leap of faith and then budget for any failings that might come along later.
Don't immediately bash the asking price, sometimes money waved in a sellers face can be a big temptation, a small reduction in asking price due to something like a worn rear tyre seller didn't mention on their advert. Then is fair to ask for a reduction of perhaps £100-£200, if both parties are agreeable.
Getting the bike home, if MOT, ride able take a long road back home, to iron out anything that you feel needs improving, that way it's far more easier to spot issues than say on a 30 minute test drive, that few owners now allow. Buyer beware!.. make sure it's what your after and satisfies your checks that is a good one.
One last thing to think over, how much has been spent in the owners time with the bike, important question as this brings you to the services and work done, while in his ownership.
Most people on here will have spent time and money improving, servicing possibly more often than necessary to their bike, that they have tended too in a long or short period, like a family member.