I know it’s natural to want to cast your net as wide as possible and to strive to warmly welcome all newcomers. And, yes, it’s correct that we don’t truly know what a user’s actions are going to be until they hit your site. But I can tell you that after a few weeks, when you start seeing the pounds going out for click-throughs that aren’t converting, you tend to lose whatever egalitarian views you might have had and come over all fascist.
Negative keywords give you some freedom to limit the kind of searches, and therefore the kind of user, you might otherwise attract.
Negative keywords allow you to specify when you don’t want your ad to be shown. In the example of Logo Warehouse, I charge for the logos on offer, so I want bargain ...