High mileage bike, but lower mileage engine - would you?

[Fazerider]

That topbox may be huge, but it doesn't mean it's knackered the bike. If it's been used for blood/organs then most of the volume will be taken up by insulation and it'll certainly be lighter than a pillion.
Fazers are decent reliable machines and I certainly wouldn't start with the viewpoint that there is a huge list of parts that need to be replaced... chances are the owner kept on top of the maintenance since the bike was doing an important job.
Most people are scared off by a high number on the odometer, that should give you good bargaining power, even if you can't find anything wrong with it.