Which of the following best describes a payment based on sales performance?

The best description of a payment based on sales performance is a percentage of sales made. This type of compensation structure directly ties the earnings to the seller's success in generating revenue, incentivizing them to increase their sales to earn a higher income. This aligns the interests of both the salesperson and the business, as greater sales directly contribute to the company's profits.

The other options represent different compensation structures. A flat rate fee for services does not vary with sales performance; it remains the same regardless of how much is sold. A fixed monthly salary also does not depend on sales outcomes and guarantees a set income without connection to performance. A bonus based on company profit, while tied to financial success, is generally not directly linked to individual sales performance but rather to overall company earnings, making it less focused on the performance of an individual salesperson.