I hope it has every option including navigation.....Because hes about $4,000-$5,000 above Kelly Blue Book Value!!
My suggestion is when you book a vehicle you need to consider condition inside/out. What options are included Nav, Spoiler, Uprgraded wheels etc. How it runs, How many owners, And what maintainence has been done!! $12,000 is what my 2001 GS430 Blue Books for. Keep in mind also he may be booking it at "Retail", And he has to book it at "Private Party"! Hes not a dealer, and unless hes offering you a warranty he cant ask what hes asking PERIOD!!!!!!! So at $12,000 that sounds like Retail......
As far as reliability and longevity these cars are built for just that!! Its not a BMW or MERCEDES. But prices for parts can be above average but it is a LEXUS, and overall from what im seeing they can run over 300,000 miles with ease as long as there kept maintained!! And yes I believe the timing belt and usual maintainence needs to be done at this mileage....Unless the current owner has addressed everything!?????
Again the values im getting on KBB.COM are as follows:( "FAIR" $7,075 / "GOOD" $7,850 / "EXCELLENT" $8,475 )
And rarely does a car fall under excellent condition!! But go ahead and do some research you will rarely find a Lexus owner that is unhappy with their vehicle, And on a scale of 1-10 I see the average being 10 as far as quality Not many complaints about these cars that ive seen (lexus gs)!!
Hope I helped!! Good Luck