The grading system is not the same at all of the auctions.
Here is an example from CAA Nagoya
9 under 1 month old, has travelled less than 500 klm
8 under 6 month old, has travelled less than 3,000 klm
7 under 12 month old, has travelled less than 10,000 klm
6 no need for any repair both interior & exterior, extremely good condition
5 in good conditin both inside and outside, possible to exhibit with slight repair.
4.5 any age, mileage, possible to exhibit with slight repair, or already repaired. Almost same condition as grade 5
4 any age or mileage, no corrosion, repaired well, possible to exhibit with slight repair or exchanging some parts.
3.5 any age or mileage, need to be repaired, corrosion or repaired trace in back panel or front buffer.
3 condition inside and outside is bad, have lot of rust, corrosion, the repaired trace or completion is bad, may have slight scratches( F inner or trunk floor, flame, repaired or little distortion.)
2 terrible rust, corrosion, need to repaired a lot inside or outside. inferior , valueless
1 inferior car, reconstructed car (no-application or doesn't appear the reconstructed part which officially recognized.)
A repaired (accident car) calamity car (flooded car etc.)
You should also consider that my most recent Skyline R34 GTR VSpec II came with alloys, Nismo twin plate, HKS GT 2530, Mines ECU + airflow meters, Nismo Intercooler, Apexi radiator, Aragosta adjustable suspension, Apexi exhaust, Mines ECU, cams, elbows and downpipes etc etc and was graded 1 at USS Tokyo.
Modified cars fall outwith the normal grading system, but are generaly the best buys.
The above extras added about 400,000 yen to the cost of the car, roughly the cost of the turbos.