You've worked hard to bring together the best offering of goods to sell at your online site. You have enticing photos. You have compelling copy. So why can't you get your shoppers to do that one last thing: push the "Buy" button? Selling is of course a practice of persuasion, and it means that you have to be absolutely persuasive in every aspect of the act—and that includes the design and placement of your buttons. Here's what you need to know about that "Buy" button and what you can do to make it irresistible to your shoppers.