I don’t think it’s that easy even if it was a medieval period. I would consider to laws, permits, Tax etc. Without these the noble under the towns jurisdiction can confiscate all his earnings. But because it’s in its initial phase they may go undetected but once his business starts booming or has a history of illegal activity such as above mentioned he can expect fines, and have his property and finances confiscated. The smart thing to do is talk to business owners ask how they started and the necessary legalities. It can be a small business owner, he doesn’t need to ask some CEO of a big company that won’t give him the time of day. The point is to start-up.
Honestly he’s put no research into the business he’s going to. This is a major flaw in the story, to be successful is not as easy as having an idea. Laws, regulations, taxes, building trust, building connections, etc. There’s more in depth topics I am not aware of which lawyers or certified professionals could cover. If you were to start a business without any knowledge and break a law you can imagine the consequences.
This is not meant to be hateful in any way. This is meant to be informative.