I walk a dozen or so large art fairs every year and have seen so many blown sales by artists that would make you sick. Mainly because the artists just can't stop running off at the mouth.
Bill is absolutely right with his comments. When you have a warm body anywhere near your ready-to-sell art NEVER discuss your web site, future work, education, gallery existence, magazines you've been featured in, photo gear, scene location, their photography prowess, the weather, their cute poodle they're cuddling, or the dripping ice cream cone their offspring is slurping over your print rack. Well, you may want to quickly cover the print rack with something.
Point is you have paid good money and time for that minute or two they're deciding to spend their budget on your work. Some customers do need to have direct questions answered. But the more you limit your vocabulary to "Cash or Charge?" the better off you'll be.