If you are going to make players earn something for their PCs, then the rules should be clear and straight-forward, and readily available. I concur with Faraday and Surreality here.
If there is discretion involved, the exercise should be consistent. Ideally, deviations in that consistency should be adequately documented to explain the deviation, and why it was fair.
These rules are different than rules about on-game conduct. Those rules are by necessity and circumstance going to need to be more vague, but should still adequately inform new players as well as provide staff the discretion to act on novel situations.
But system-based gains should be less discretionary and more strict. Otherwise, you’re going to have favoritism complaints, among other things.
Staff need to be quick and decisive when they act, regardless.