Guess you have the performance-linked incentive in place already where there is a % bonus on sales as commission given to floor shop employees.
For high-value products, you can provide employees with some branded items of a particular value of their choice. You can also offer the product at a subsidized price. You will need to differentiate between ordinary and high performers based on the eligibility of the amount. The best performer can act as a shop supervisor for a day through job shadowing. This measure helps employees understand the issues associated with a managerial role while feeling rewarded for superior performance. Job rotation across various floors or product categories will help in curbing the monotony of selling the same products.