Cluster sampling is a type of sampling method . With cluster sampling, the observer splits the population into separate groups which are called as called clusters. After dividing the whole populations into clusters he select a simple random sample of clusters from the population. The observer conducts his analysis on data from the sampled clusters.
From the given statement we can see that the automobile is doing his analysis by selecting three stores from each state (cluster) in the country and surveys all customers present in the store in a certain week.
