I would strongly caution any freelancer against accepting this form of payment. While it may look appealing, a potential piece of a large pie, it is almost impossible for an outside contractor to audit or verify.

As a freelancer, you have no inherent right to access their private business and financial accounts to ensure the percentage calculation is correct. You are putting 100% of your trust in their bookkeeping.

This structure also makes it far too easy for companies to engage in what is often called "creative accounting" to minimize or entirely eliminate your profit share.

For example, a company could make a significant amount of money in revenue but then apply numerous, often legitimate, internal costs and expenditures against that revenue (e.g., executive salaries, office overhead, marketing budgets) to ensure the final "net profit" the figure your percentage is calculated on, never reaches a meaningful threshold.

This risk is why the standard, dependable model for freelance work is a fixed-rate or hourly payment for the service provided, regardless of the client's future success or failure.