Out of all the Internet Retailer Top 500, I've only found one that offers incentives to web surfers who look around without purchasing. When you close your browser tab or window, a pop-up chat window appears:
It appears site visitors only have one go at the offer. If you close the box and return again on the same day it won't pop back up. Of course, it could use browser cookies and it could reappear after cookies expire or you delete them.