Even then how you you know? I don't think anyone can reliably look at a vegetable and tell you how nutritious it is. I don't think it is reasonable to have the general population being experts in evaluating vegetables.

I think what could work here is mandated labeling. This is required for most foods but generally not produce. I think there are some reasonable reasons for this, but for farms producing huge volumes it seems that occasional testing that gets reported at the store would make sense.