There is many different of customers, easy or tough.
First of all, you need to know more information about the customers, what cause they come in, what is their needs.
Try to provide opinions for the customers. Different person has different characters, so it is so difficult to set a specific way to serve all customers.
Many categorizations and variants possible ..
1. Global vs Local (depends on their physical location)
2. Tough vs Easy. (depends on their character)
3. Result oriented vs process oriented (depends on their approach and need)
Just an added suggestion - understanding the problem statement from customer and how it impacts their business will always give better insights to the problem and the impact you can make to the customer :)