Most purchases (perhaps barring impulse buys) are made to fulfill a need or to solve a problem. Looking from a broader lens, problems can be of numerous types and deviate heavily from the traditional sense attributed to them. Every product worth its salt today is made to alleviate a problem after it has been recognized and established. Products which do not solve anything, do not survive.
Much like going to the doctor a customer who has walked into a store is looking to fix an issue E.g. a customer is not shopping for a drill machine but needs a hole somewhere. It is this problem which has forced a tool purchase. Much like doctors, sales representatives should be able to quickly diagnose the underlying problem of the customer.
Once it has been established, the customer can now be offered product suggestions in a way that establishes credibility with the customer as an expert in the brand and the product. It is very easy to fall in the trap of assuming you know what your customers want and what is unimportant to them. Customers can have very different goals to achieve from a product than what they state.
The best way to get an idea is to ask questions, while mystery shopping, you will know if a representative is doing need assessment if he/ she asks any of the following types of questions: