It can establish a functional relationship with sales volume, sales quantity, sales profit, sales payment and other factors. As for the establishment of mathematical model, we should first consider the proportion of sales, sales quantity, sales profit and sales money recovery. If the percentage of commission is a%, b%, c% and d% respectively. Then:

Commission amount = sales *a%+ sales quantity *b%+ sales profit *c%+ recovery amount *d%.

If an item is not assessed, the commission ratio of the item is 0.