When I am going to sell something, what should be my main concern? Is it the customer service and relation or the company's profitability only?

the salesman should have concern with customer service and relationship.
Keep the customer relationship strong for Increasing Sales Line.

The first important concern would be about customer's NEED !

Having keep the strong relationship with customers,it is very easy to sell any product to your customers. with the hlep of best servicess and relationship any sales persons can increase his sales.