SOUNDS IF it IS VERY GOOD AND WELL CARED FOR vehicle. Will the Dealer give you any kind of warranty ?
If you go into "my lexus" on Lexus.co.uk and input the reg no. you might be able to access more information re servicing etc.
If, ok you just need to agree what seems a fair price to you.
Check M.O.T. and Lexus Service history inc. Annual Hybrid Battery checks..
If both ok, I would only be concerned about the price I would have to pay.
I would offer £4500 max.
A former member had one which he took to over 200,000 miles.