Validate customers' decisions.  Even if you do not agree with customers' choices, always validate their decisions.  If the vacuum salesperson was not able to make the sale, he could validate the customer's decision by saying, "I understand how you feel.  This brand is costly."

- Renee Evenson, Customer Service Training 101

In the last few years, high-pressure sales techniques have swiftly fallen by the wayside as sales people have found that they may result in the sale, but they seldom inspire long-term customer satisfaction or loyalty - no one enjoys feeling like they were manhandled or manipulated into a purchase.  A more effective sales technique to use after the customer has decided not to purchase is to show your understanding for the customer's decision.  After all, it is their decision, not yours.  Don't tell them they are making a big mistake (even if you think they are), but assure them that you will still be there and happy to assist them again if they are ready to reconsider.  They may not ever end up buying your original offering, but they may remember your graciousness and return to you in the future for something else or to recommend you to others.