Service History would be good starter. Not only look at the service book but also check the lexus website for the electronic history and see if it matches and has hybrid check been done every year.
Look at the MOT history carefully and see if it tallies up ti will also show any that would have cause MOT failure and does the mileage look correct year on year.
Personally i would not look at anything older than 2016 at this point, but bear in the mind the new 2017+ model have a big jump in VED tax.
Look the seat particularly driver seat, does it look really worn vs mileage.
The rest would be wear and tear such as brake pads etc.
Inspect body panel especially if its been raining, are the colours matching.
Check engine cap for mayo build up.