I don't know if I think the use of questions is persuasion or more of control. Being in control of the sales process, i.e. the closing, is one of the greatest games in marketing and sales.
I think persuasion starts with permission. For one to persuade someone, I think that other person has to give them a door to walk through.
Example.
The salesperson is talking to a client about purchasing a certain part for company equipment. The client sets the price (usually set by competitor, superior, or another).
The salesperson has to persuade by selling value and diverting (persuading) the buy towards value instead of cost.
Just a theory.
Ed Callais