Paying your consultant

How to structure payment to your consultants depends on a couple variables. Is the project they are completing a short term or one time effort? Maybe an hourly rate with a cap or a set fee is best. Is it longer term? Eg ongoing Contract CFO Role, then a combination of cash today (lower hourly rate) plus long term incentives tied to your success, such as stock options, might be more appropriate and protects your cash reserves. Anyone you can put on a commission structure believes in your business and in their own abilities. Just be carful to not over pay with too high a rate or tie commission to wrong outcomes. Earning their money will dive their behavior, a powerful management tool when crafted correctly, plus you are only paying them out of what they bring in.
Ask you CFO for advise.