Is it permissible for a manager to import goods for his personal account and then sell them to his company for a small profit, given that the selling price is less than the market price?

It is not permissible for an agent to buy from himself unless he has the permission of his principal, because he is entrusted, and he may have two conflicting interests: to buy cheaply for himself and to get the best quality for the principal. However, if you are not an agent for purchasing, it is permissible for you to import goods and sell them to the company, provided there is no cheating or deception, and that your work is outside official working hours.