Wondering Whether A Domain Name Purchase Is Worth It To Make Some Money.?

Ok i’ve never did this before so thats why i’m asking questions but I have an idea and am looking for advice on whether or not to purchase a domain name to try and resell. Say I know of a company call Johns and they specialize in muffins. (these are hypothetical cause I dont wanna give my idea away). At the moment they own the domain johns.com but somebody else out there has johnsmuffins.com and just has one of those fake stupid google searches. Now say the company is changing its name jills. Well jills.com is alreayd taken but jillsmuffins.com is not. This is a growing company. Would it be worth it to take up that domain name? What would it possibly be worth? To try and resell it would I have to promote it or would somebody likely contact me? Advice would be awsome!