How does condition grading work?
Pieces use the hobby-standard TCA-style grading scales, split into three separate things so you can be precise:
Model (item) condition — C-scale
How the model itself looks, from C-10 (Mint) down to C-1 (Junk). C-10 is factory-fresh and unrun; the numbers step down through Like New, Excellent, Very Good, Good, Fair, and so on.
Box condition — P-scale
The packaging is graded separately, from P-10 (Mint) down to P-3 (Poor). A great model can live in a rough box and vice-versa, so they get their own grade.
Operational condition — O-scale
How it runs, from O-5 (Like New) to O-1 (Non-functional) — useful for engines and anything with moving or electronic parts.
Why three grades?
Buyers and fellow collectors care about different things — appearance, originality of the box, and whether it actually works. Grading them separately tells the whole story at a glance.
Related: What's the difference between box condition and shipper condition?