Mining rigs- How some are making extra money?

You probably heard of people setting up a mining rig and making money trying to be one of the first one to crack the calculation to get s certain percentage of that coin they're mining for. . But have you heard that people are making mining rigs and selling them for a good amount money online. Yes that right some people are also making money selling the tools that are involved in been able to mine. Your probably wondering why, well its do to the fact that not that many people know how to set a rig and dont know what specs are best when you're mining for crypto currency. So instead of building one they're own they go on the Internet and look for people that are actually selling them, but they're not selling these rigs cheap and a-lot of times people don't really care how much they're paying for it just that they know they'll be able to get start mining for they're prefer currency and feel like it worth it in the long run.