There are multiple ways to do valuation. It takes into consideration the business sector as well. In case of commission in other word the revenue in your case, you can try the following models which are widely used. A) Revenue multiples B) Traffic Multiples C) Earning Multiples D) DCF analysis and E) GMV
In recent times, we are seeing a more significant number of early stage e commerce startups presenting their valuation based on GMV. But the biggest limitation of GMV is that it is based on gross orders and does not account for adjustments like returns, discounts, rebate, cancellations and cashbacks. It is not ideal to set a benchmark on GMV multiples as it highly depends on your business model. GMV often can be skewed by product mix and offers no insight into the value of the business.