As a product manager, you could be asked to visit customers to help close a sales deal or to trouble shoot a customer problem along with a technical support person. None of these visits can be considered as part of your effort to listen to the voice of the customer. This is because in either of these cases, you role is to overcome the customer’s objections to close the deal or to find workarounds to the problem faced by the customer. In both of these cases, you are not listening to the unmet need of the customer, you are trying to sell or get your product to work. You are the one who is doing the talking.
When you visit customers to listen to their voice, you should be listening and not talking. Human beings cannot do both of this at the same time (sales people may think otherwise !). When you are visiting customers to listen to them, your role is that of an explorer. You have to keep your eyes and ears open. Customers do not always tell you the whole story, not because they are withholding information, but in many cases sometimes they themselves do not recognize the pain points they have. It is up to you as an explorer, to ask the right questions and to get the customer to tell you their real problems (not solutions) that if solved would create a product differentiation for your product.