There's no 1990 Q on the planet that's worth $8900, even if it was one of the "0-mile" Q45's from Nissan's collection. That guy is clearly having heat stroke, he needs to go inside to the A/C and come back to reality..
Honestly mileage doesn't mean a whole lot to me on these cars. Condition is paramount. Regardless if the car has 8k, 80k, or 180k miles, there's a ton of stuff (rubber suspension parts, hoses, etc) that all need replaced.
One thing that would concern me on AZ cars is if the interior is dry rotted and the paint condition.
Over the last year I've seen a few 1st gen Q's with sub 100k in really nice condition, and I doubt any fetched over 5k.
Have him post up the list of stuff that's been replaced, and I/we will be the judge if it's been "fully restored".