The problem with rules around income is that it requires information a sporting body wouldn’t/shouldn’t have access to. It’s none of their business how much money I make. I’m surprised anyone would endorse a rule that would effectively require all competitors to reveal their income and income sources, unless they wanted to compete open.
Rules around performance can be made based on data that they (theoretically) have access to: competition results. It still won’t be perfect, because there are people who train at home and rarely compete, then come out and win championships. But the idea is to factor in the level people have competed previously and scores obtained to classify them as essentially beginner, intermediate or established at a given level.
From British Dressage:
Each level of competition e.g. Preliminary or Novice is divided in to three sections Gold, Silver and Bronze. The section into which a member may enter is determined by the horses and rider’s experience and points won at each level of competition. Each level will run as one class with all riders being judged by the same judge. At the end of the class, for results and qualification purposes, the class will be divided in to the different sections.
- Bronze sections are for less experienced horses and riders who have just started competing at a given level so that they can compete against those with a similar ability.
- Silver sections are designed for those combinations that have achieved more ability at a level and have demonstrated that they are no longer a beginner at that level.
- Gold sections are for riders who have gained experience at higher levels and are riding a horse with less experience, or for combinations who have demonstrated that they are competent at a level. There is no obligation for a combination to move out of the Gold section at any given level should they not wish to compete at the levels above.