In supermarkets, stores, regardless of what is offered in them, can always arise issues related to the proposed range.
On how correctly you will talk with the seller determines what quantity and quality of the information is received on the proposed product or service offered.
Properly question. You always have to understand that specific question meant by a concrete answer. But in order to be able to ask this question, you may need to learn at least the basics of information on the proposed product or service. This will not only orient itself correctly in the proposed range, and, if necessary, to allow the seller to more intelligently respond to the questions put to him.
Politeness. If you talk to seller polite, not as a servant but as an equalperson, the seller will treat the customer with respect and understanding, and, if anything, will be able to choose from a range of goods or services is just what you need.