The saying means that there is a high risk of losing a customer by talking too much, but there is no risk of losing the customer by intently listening to them or listening too much (if there is such a thing).
The phrase points to the importance of listening rather than just talking when engaging a customer. For instance, a salesperson who talks a lot about the product, its benefits and why the customer should buy it may likely not make the sale. However, the salesperson may take the time to listen to the customer and adequately respond to their concerns. By understanding the customer and addressing the customer’s concerns, the salesperson may then get an opportunity to pitch the product as a solution, and not just an opportunity to make a sale. When one listens, they get a chance to understand and respond sufficiently and appropriately from a point of knowledge. The phrase implies that one cannot do too much of listening but rather accentuates the need for it.
There is a difference between hearing and listening. Effective customer service skills include having effective listening skills. Listening requires focusing on what is communicated from the customer with an open mind and great amount of attention. A powerful way to connect with a customer, especially an irate customer, is to just listen and knowing when to respond with the appropriate verbal acknowledgments.
Good listening involves paying close attention on how the customer is communicating the problem by listening to the tone of the voice and the language (non-verbal/verbal). Sometimes an empathetic acknowledgment to a customer complaint can come across inappropriate because of the timing of the apology. All you hear is how upset the customer is and you are trained to be empathetic and give an apology. However, rushing in an apology before the customer has fully explained their discontent may come across as rude or robotic. This is what happens when you only hear what the customer saying and not listening to the customer to know when to chime in an apology. This is when the loss of a customer could be the end result.
Most customers prefer to feel as though the person selling them a product is engaged in their own wants, needs, and interests. A salesperson who talks too much often gives the customer a sense that the only thing they are interested in is making a sale. Listening to what the customer wants to talk about can help in several ways. The tone of a customer's voice helps the salesperson discern the customer's mood and interest. The topic they choose helps in determining how engaged the customer is in the demonstration. Listening and responding appropriately creates a bond. No matter what the subject is, listening carefully may reveal clues about what a salesperson should use in their final sales pitch.
The "talk yourself out of a customer" part comes from talking over them and just trying to "close the deal" right away. Customers already have their guard up when making initial contact with a salesperson; you have to listen to them explain what they are looking for and then go from there.
I have done sales and worked at a commission-based position. When trying to get to the root of what the customer wants, you want to listen the customer, not just hear them out. The customer is talking to you for a reason; they have already gone through their needs/wants analysis and they want you to convince them they are making the right decision. By listening to the customer, you make it easier for them to identify what it is they actually want and then you can help them reach that need by providing your goods/services.