PortForward.com sells software that will set up your router for you.
But they also give away the complete instructions to do it yourself. For free. They give away instructions for every router, every model. These are the complete instructions with no “gotchas”.
Why? Because they get a TON of web traffic from search engines. They have a zillion fans.
And anyone who doesn’t want to bother doing it themselves can just pay the $30 for the software. And people who were looking for a free answer weren’t going to pay anyway, so nothing is lost.
Lesson: Sometimes your best promotion isn’t selling. It’s giving.