Both plumbers and factory owners do indeed have opportunities to exploit people. But my plumber friend can only exploit one customer at a time, where as a factory owner multiplies that ability. Multiplication is a powerful operator.
A plumber can exploit a customer by charging an exorbitantly high rate for work. They can choose to exploit their position of power as a supplier of services where a customer has an urgent need.
Exploitation is not charging a high rate for work. It is charging a higher rate when a customer is not in a position to shop around.
It's hard to know where to start with things like this. How does the plumber exploit employees? Why are you assuming anyone exploits anyone by default?
Customers don’t get exploited in this way. They generally are also employees of some company that does exploit them, but that is a separate relationship.