Hi and welcome to ukcougar.com, your in the right place for all things cougar related, as well as some crazy banter. You will also be able to find all the fixes you need in our subscriber sections. Have a browse around the open forums and get a feel for the place. Remember! ukcougar.com is the only workshop manual for the big cat.
Take it for a good blast on a duel carriageway or motorway if possible, drive it over some bumpy surfaces and listen for little knocks and rattles, although usually these are not serious but worth noting (suspension bushings)
When you first go to view the car, take note of the ground under the engine, are there any serious looking oil spots etc. Also look under the rear for the same thing, dealers trick, they turn the car around so the leaks don't show at the other end

The steaming pot under the screen is ok when you have the car at home, but not really viable when it's sat on the sellers driveway

I wouldn't say the screen heater is a big issue anyway.
In general, if the car "feels right" it probably is, and any minor dings from supermarket trolleys etc are to be expected on a ten year old car, just check for badly repaired paintwork.
Pay special attention to the underside as already mentioned, especially the jacking points along the sills, don't be afraid to get on the floor and look up from below.
Good luck with the viewing and hope it is a good one.