If possible buy from a Jaguar dealer with a 2 year approved used warranty. Check everything as you would for any car, but especially all the electrics. Make sure it has all the options you need, don't think it's bound to have xyz. Check any service history/advisories.
2012 XF Premium Luxury 3.0DS in IRR
Previous 2010 XF Luxury 3.0D, 2002 S Type 3.0 S (Petrol)