I rushed into buying mine earlier this year at a time when my wife was about to go into labour and I really liked the car - I wasn't at all cautious and bought a 2003 rx with about 95000 miles and no service history whatever. It is a 98-03 model with the spare wheel in the boot and does not have roof bars. I can get some after market ones for it though, the lexus ones are like hens teeth. I had to have a bit of work on the brakes, I think because it had been sat for a while, and it is currently being converted to run on autogas. We had looked at merc ml's and found them to be rusty sheds, the lexus by comparison, although older and with higher mileage, is like a brand new car.
If I had had a few more pennies I would have gone for a lexus approved used, but that is in hindsight and I couldn't have afforded it anyway.
Since buying it I wrote to the previous keeper and he has given me the detachable towbar and the lexus boot liner - restored my faith in humanity actually, he could have just ignored my letter but he took the trouble to get them to me!
Check if the cam belt has been done, I have no idea if mine has so I will have to get it done next year.
Also check if the sat nav computer is present, it should be in the boot under the floor. If it isn't he here the screen for the sat nav will say "external device not connected" or something similar.
There is loads of help on this forum as to what to look for, best of luck.