Val, G., Jeff, G.(2007).Open question selling : unlock your customer's needs to close the sale... by knowing what to ask and when to ask it .:McGraw-Hill.
Gaya MLA
Gee, Val., Gee, Jeff."Open question selling : unlock your customer's needs to close the sale... by knowing what to ask and when to ask it".:McGraw-Hill,2007.Textbook.