I too hadnt much idea when I went to look for one.
I simply tool it for a test drive and checked everything out. There were a few things I found that I wasnt happy with.
One was the way the high/low worked. The car I tested was an auto and it seems you need the car rolling a little, put the main box in neutral and then select low/high. Put it back in gear after of course.
The other thing I found was the electric window didnt work. Check them all
And of course, oil leaks. Landies are full of em, have a good scout round underneath.
It will need a long MOT too, even if it gives you time to sort out the niggles you find along the way ;)
Enjoy it though, they are a cracking motor :D