Is it permissible to sell a commodity (such as a truck) at a price higher than its market value, given that it is operated by a company and guarantees income for the buyer?

Selling a car at a higher price than its counterparts because it operates within a specific company is a valid sale; this is an advantage of the car, not a condition of the sale. A void condition in a sale is to stipulate that the buyer must keep the car operating within a specific company. This condition contradicts the essence of the contract, and the buyer is not obligated to fulfill it.