how to restrict sales of item to specific customer

Question:
Say I have 30 customers and suppose i want to sell my product for 2 customers only
I don't want to sell for others.
how can i do it?

Answer:
1. Make one group of customers to whom I want to sell the particular item.
2. On price-list form Qualifier (tab) add that group for that item line with desired context, attribute, operator, and value