I think the difficulty with that is that different conditions are subjective for different collectors. I don't care if a pony has a small haircut, for example, but that is a dealbreaker for other collectors. I don't like when hooves have markings, but that is not such a big deal for others. I think I would just have a form that describes the condition of each part. Like hair, paint, and body.
Pricing is difficult, I would just figure what you are okay with letting the pony go for and be open to offers.