Aside to all the bits covered.
Don't put too much in the FLSH. Whilst it can be perceived as being a good thing, and generally it is. I find it a bit questionable and unreliable in some areas that cause concern, for me at least. For example, the air filter is scheduled for changing every 35,000 mls (utterly ridiculous). If (as I experienced) your car is at say 66,000, then Lexus won't even lift the lid to look at it. That is plainly not good practice!!!!
Lexus services will never look at the slide pins in the brake calipers....again, ridiculous!! They would rather hit you for 400 a corner to replace seized brake calipers every 30,000 mls
If the vehicle has around the 60,000 mls or is 5 to 6 years old then ensure it has had the big service including the spark plugs changed (often referred to as the 60,000 service)
If the vehicle has the Mark Levison/sat nav/ reversing camera screen. There have been a few reports of touch screen break downs on the pre face lift models (55 - 09 plates). If you look to Lexus it can be £2000 or more. You can find replacement screens from the far east on Ebay. There are some accounts on this forum of how the screen was replaced.
Take a look at the water pump and look for leaks at the pulley .... another known issue.
Take a good look at the exhaust...very very expensive and not available elsewhere thus far.
Talk to the owner and you can very rapidly establish if the owner has a care for their car or not.
Best of luck. They are jolly nice cars.