Sorry, in answer to your question.
1st thing to do is ask the owner when the water pump was replaced, try reach down to the waterpump auxilary belt, have a pull of it and check for any play, if you can wiggle it then it could be a sign the bearings are gone.
Check the pipe work at the ends for any fraying, most common fault with the pipes is for them to burst at the jubilee clip, most common fix is just for people to cut back the damaged bit of pipe and reattach. Not good
Check the radiator for any warping, its hard to get a good look but keep trying, a new radiator is 250euro and if its warped in the slightest it will need to be replaced.
The other thing to check is the radiator housing which is attached to the coolant resevoir, any signs of cracks or fraying, particularly at the neck of the outlet pipe. Thats the pipe attached to the housing at the top of the radiator. If you have a squeez around there and just make sure there is no flex or bend in the plastic neck that the pipe sits onto.
Anything else you have to do is just make sure you ask the seller as much questions as possible and try trick them out by going back over questions subtly, if they are telling you lies to sell the car, chances are they wont remember what they told you 10mins ago.
With the rust, it is usually obvious and you will find it around the wheel arches or else paint bubbling off but you will also need to check under the wheel arches, if there is no rust then make sure there is enough underseal on them. Also check the boot, if the battery is in the boot than try run your fingers under it to check for leaks, also lift up the spare tyre and look for rust/leaks there.
After that they are fairly bullet proof cars and when buying just do the normal checks you would do when buying any car!!
Hope this helps you.