The most successful web developer I know only makes websites for GYMS, he knows how to craft the ultimate gym landing page. He knows what gym owners need, what they respect. And he knows what they're naive about, and what struggles they have to overcome. He knows how to sell and market to experienced fitness experts, and fresh soft newbies alike.
There are millions of gyms, and he is an expert and his knowledge could help every single one of them. And guess who comes looking for him specifically, when they want to start a new gym business? The pro "gym websites" guy, that's who, who has 20 Gyms in his portfolio and 20 blog posts about how to be the best gym owner possible.