I was reading an article on entrepreneur.com about negotiating deals and the first rule seemed particularly relevant to retailing.
That rule was "Always start the negotiation". The writer explained that to get the upper hand in the negotiations you needed to set the agenda.
In retail, if you let the customer ask the first question the best you can hope for is "May I have one of those?" However the first question may also be "What is the best price you can do that for?" and then your negotiation becomes bogged down on a price discussion.
By getting in first, traders are able to ensure that the focus is on a range of product benefits, not just price. Maybe something like - “Can I give you a little rundown on that product? If you’d prefer not, I’ll leave you to browse.”
Seemed like good advice to me.