Is it permissible for a sales representative to sell goods for his own private account without his company's knowledge, using its vehicle for delivery?

If the representative uses the company car and carries out private tasks outside official working hours with the company's permission, then there is no harm in it. However, if it is during working hours, then his action is impermissible, because his time belongs to the company. Similarly, his use of the company car without its permission necessitates compensation, unless the company permits it.