Pretty obvious when it's written out like this, but it seemed like a revelation when I discovered it.
Enter a URL in alexa, click on bounce rate, then go to clickstream to see where their upstream and downstream traffic is going (also determine what their redirect URL is). If your landing page bounce rate is 80% and theirs is 50%, and their clickstream traffic is going to/from the same referring sources as your's, you'll know why your margins are lower than you expected them to be...
Enter a URL in alexa, click on bounce rate, then go to clickstream to see where their upstream and downstream traffic is going (also determine what their redirect URL is). If your landing page bounce rate is 80% and theirs is 50%, and their clickstream traffic is going to/from the same referring sources as your's, you'll know why your margins are lower than you expected them to be...