Poor service after the sale. Eliminates referrals, makes the salesperson look bad, reduces pride, causes belief in the company or product to diminish. Inability of product to perform to claims. Your salespeople must develop a belief system around a product, or it can't be sold. Unfulfilled promises after the sale to the customer.
Salespeople feel personally responsible for the promises they make.
Negative attitude of the boss. Grumpy boss equals low morale, equals high staff turnover. Bosses create their own fate. Fights that no one wins. Production fighting sales.