Apple already knows who is installing which apps and when they are executed. So they can easily tie it back to the developer and simply bill them. And if they

Apple already knows who is installing which apps and when they are executed. So they can easily tie it back to the developer and simply bill them. And if they fail to pay the bill, Apple can (a) disable their developer account so they can't sign new apps or (b) add them to the server-side block list that they have been using for spam/malware on OSX for years now.