People who patronized liquor sellers are called guests. Before those people can be served, the bar man has to decide whether to sell drinks to them or not. Some factors that make one unqualified to buy drinks include: under-age, intoxication, pregnancy, etc. So, the bar man has to assess the guest and decide whether to sell to him or not. Thus, when you are assessing a guest, you are: considering the age of that person, you are determining whether the customer is already drunk, you are checking if the customer is pregnant, if female, etc. When you are assessing a guest, you are getting information about the behavior of the guest.
