Hi Richard,
Pictures can look nice....that car is a 'carbon-copy' of my car before the start of my rebuild from 2021 to 20??

. Great colour and wheels, but not a great fan of the rear spoiler.
I can not see much history in the adverts description apart from 3 owners and 62000,so just 'run-in'.
There has been lots of info and articles in the JEC about these later cars ref; Darren's fantastic rebuild of his Flamenco Red car. You are in the best club.
Mainly, if you have no experience with XJS's, you really need a XJS specialist to look it over.
I am not too sure if Clarkes Restorations who are a hour from Horsham offer this service. They have very good cars and buy a few from dry US states etc.
If you buy it, do you have the experience and tools to work on it yourself or can you entrust in a good Jag specialist?
These cars can run away with costs dramatically.
A large history file and long ownership can go a long way (not always though.)
Even though these late cars were 40% galvanized at the factory....30 years hence has past and even these late facelift cars can now be rotting badly in the UK climate. I can vouch for this, as I am rebuilding mine now (welding all finished) and discovered quite a few unseen rust areas, underneath things you only see once you take it apart in certain places, but probably not as bad as a 1977 XJS, similar age to your old car.
How would the top windscreens scuttles be?...has it had a fresh coat of paint in this spot or anywhere else?... questions I would ask.
You really need photographic evidence of any metalwork carried out .
If you get a good one, they are great classic cars as you probably already know. I think prices are more realistic now and getting rare on the roads now.
Good luck in your potential XJS purchase.
Kind regards.