The bulkhead is probably getting a bit tatty. Check for rust outboard of the fresh air vents. Also get a screwdriver and take out the drivers side speaker (if it has such luxuries) by the drivers right knee. You will probably be able to see the engine from there. If you cant, buy it. If you can, knock him down £200-300, and buy it. Mumbling about rotten fruit helps here.
Engine wise, take off the oil filler and look inside the rocker cover with a torch.
The colour will tell you what the engine is like. Black treacle - walk away, black but clean - walk away slowly, dark brown - don't drive it far without RAC/AA Recovery, Strong tea - should be OK for another 30,000 miles. Anything lighter than tea - the engine has been replaced in the last 50k and well maintained.
Hope that helps.
BTW Same conditions as Jono apply, no tears.
"A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools" Douglas Adams