Especially if you are selling a large product online, Internet stats show that someone will not make a purchase until they have been to your site 3-4 times. Because of the speed of Internet, people are doing a lot more research before making a purchase because it is quick and easy. Have your site setup to get an email address, phone number, name, something. Not only will you get an additional piece of data to market to this person down the line, but them giving you information is getting them to commit to your website just a little bit more. Sometimes, that little bit more will have them come back to you, versus a competitor. Offer a coupon, enter them into a sweepstakes or just offer up good information on a monthly basis.