Assuming you've done everything properly leading up to the close-meet and greet, qualification, product presentation, intelligent sales questions-confidently look customer in the eye, present numbers, and ask when they would like to take delivery of product. Then wait until they speak. Either you have a deal or they will say no, at which point you ask why not, overcome the objection and ask again when they would like to pick it up. Or if it is a smaller item ask would you like it gift wrapped, inscribed, etc. NEVER ask a yes or no question.
Bear in mind though unless you've done a thorough, professional job in laying the snare, you probably won't close them with a single closing question. The close starts at hello, and you never stop qualifying.
