Great post.
I'm sure I saw you wrote some buying advice for another guy in here but just can't find it now. I've written what I can remember and added a few more suggestions :)
Check the oil to make sure its oil and hasn't got anything else in it, like water/foam I checked a car recently and the dipstick was bone dry!!
Check the rad to make sure it's got water in it and not mixed with oil.
Ask them for the last MOT test number from the VT20 test certificate so I can check the MOT history (&Mileage) on http://motinfo.direct.gov.uk/internet/servlet/ECHIDDispatcher
If you have any suspicions that the clutch may be iffy, here's a simple test you can do while accelerating from a stop. Put the car in first, accelerate to normal shift point (3k rpm is mine). Shift to second and go back to about 3250/3500 rpm. Instead of hitting third gear, try to put the car in 4th gear. Once it's in gear, floor the gas pedal. If the clutch is in good shape the car will kind of bog down and chug along as it picks up RPM then will come alive at about 2800 rpm and feel strong. If you put it in gear, floor it, and the engine seems like it's revving out and starting to really get going but the car is still sluggish and is not accelerating proportionally to the engine RPM....start asking questions, this is a sign of excessive clutch wear.
Buy with your head and not your heart
I'd also add, assess the owner and his house not just the car. You'll get a good idea how he treats his car by looking at how he lives and acts and also by just talking to him.
If something seems too good to be true be very wary.
If something doesn't seem right it probably isn't. Buy with your head and not your heart.
Try and see and test drive a perfect/excellent version of the car you are looking for before you start looking. You'll then know what one feels like to drive. Friend might help?
If it's a dealer you can ask them whether they have done a HPI check to see whether it's been stolen, written off etc. Me personally for piece of mind I'd always do my own HPI check, its only about £15 after all :)