questioning is traditionally treated by conventional sales people and conventional sales training as a process to gather information to assist the sales person's process, and this is how it is typically positioned in the old-style 'Seven Steps of the Sale'; however, modern sales methodology treats questioning in a radically different way - as an essential part of a facilitative process whose purpose is to help the buyer decide (see the information about collaborative selling and buying facilitation for more explanation)
questioning is a fundamentally important part of selling - techniques being increasingly developed and refined far beyond early selling techniques - transferable to and from other disciplines (notably coaching, counselling, therapy, etc)
see for example Sharon Drew Morgen's excellent facilitative questioning methodology and the Clean Language concept