You must always understand that the sales person you assigned to a customer must be the one who performs the miracles for him. You want the customer to automatically think of your sales person when things go bad, because they trust he will resolve it for them. When he solves problems for that customer, he will be called first to place new orders which will grow sales. When you take him out of the connection to the customer, his requests for new orders is diminished because he is seen as out of the loop, unconnected to those who make decisions. Include sales people every time there is good news to relate to the customer. It will always pay back in far greater returns for the company.