Welcome on board mate.

59000Km is more or less within bounds of average for a ten year old bike and not a huge amount for an XT, so I shouldn't necessarily worry too much about that (service intervals are annually or every 10000Km). Go for a ride and see how it feels. Generally you can get a good feel for whether a bike has been looked after by looking at its cosmetic state and the things that are easily neglected - chain and spockets, brake pads, tyres etc.

The XT engines are pretty strong and other than checking for the usual stuff (odd noises/rattles/knocks and the colour/condition of the coolant and oil), you should be OK there too.

The things to watch for are more related to the chassis and suspension. Get the front off the ground and check for notchiness/play in the steering, also do the same at the back and check for play in the linkage/swingarm. Look at the operation of the shock and forks too. Also some electrical connectors are prone to corrosion, so check everything works and the battery is charging within spec (13.6-14.4V).

There's not really much on an XT that would be uneconomic or difficult to fix, just make sure anything that needs sorting is reflected in the price.

__________________