In my selling workshops, I always ask delegates: "If you are going to a shop, and the salesperson asks you if he or she could be of help, how many of you reply by saying: Thanks but I am just looking?"
Generally they all reply in a similar way. Now explain this. These salespeople in my workshop, who are convinced they are doing a great job helping their customers, they themselves don't want the help of a fellow salesperson!?
The simple explanation is that no one wants to 'be sold upon'! We all want to believe that it was us, who bought, instead of being sold to.
It isn't different with our buyers, if you give them the feeling you're here to sell to them, they will put up that wall of defence, which will be very hard to tear down afterwards. Instead, give them the feeling they are still in charge of their own decision process and you may have a smoother journey to the closure of the deal.