What should a salesperson do when customers become disagreeable? This largely depends on the situation – who is this customer, how long have you had this relationship, and what's the nature of the disagreement or complaint? Very often, customers harbor complaints that can actually provide salespeople with valuable feedback about how they're communicating or what kind of products or services would be a better fit. Try looking past the tone or attitude and see if there's anything you can take away from the situation that would end up serving you well in the future. No matter what (even if you decide the customer is more trouble than he/she is worth), always maintain your professional attitude and demeanor when responding to a customer who's disgruntled. Keep a level head and do your best not to lose your cool.