Make it easy for your customers to complain or give you compliments, ask about installation or proper use of the products they bought. For certain types of products, you need to follow up with a telephone call to ensure the customer is satisfied with his purchase. Does he have questions? Is there anything that is not working or does not seem right with installation? Touch base with the customer after the sale. send them a technician free of charge as a followup if necessary to make him happy and content. As a followup and with their permission, send them catalogs, sales brochures for associated products they may find interesting.