In a double-sided marketplace I'm tempted to think of the actual seller as being the one that determines the price.

In the case of Handy, Uber, etc... it is in fact Handy, Uber, etc.

In the case of Amazon, the price is determined by the contractor themselves.

Is there some major flaw in this thinking? Employees are not generally empowered to determine the price at which their work is sold, and yet contract suppliers are. I think this works fairly well to determine whether or not the person actually performing the work is really an employee or a contract supplier.