The IC must have his own clients in his own shop
A subcontractor's "client" is the supervisor. So long as you CAN (not necessarily do) have any number of such supervisor's you are independent.....i.e.- IC does not have to bring his own work [client in the sense of bank, etc.] with him. A supervisor can and should send the IC work (fee splits). That is a normal business practice, and it helps to have a formal contract. In fact, if the trainee is bringing clients, he should be referring them to the Supervisor. Otherwise, the Supervisor is co-signing them as a subcontractor to the trainee.....If the trainee is selling his own work, he is not a subcontractor. If he is selling the work on behalf of a supervisor, it would be making the case for the IC being not Independent. He should only be pointing the potential client in the direction of his supervisor/contractor.
Client > contractor [supervisor] > subcontractor [trainee] > whomever [helper, secretary, etc.] If the contractor attempts to restrict the subcontractor from using help, he is not treating the subcontractor as a subcontractor but as an employee.
If an appraiser has an overload of work, he might consider taking on a trainee to handle that overload. If the appraiser is expecting the trainee to bring along clients and assignments with him, he is just an appraisal mill, imho.
Remember, too, that 99% of the time, the IRS will not become involved unless the IC arrives on April 15th with no money to pay his taxes, has not filed any quarterly taxes, and tells the IRS he "works for" so-and-so when they ask why he cannot pay taxes. And likely, 99% of the time that supervisor did not send any 1099's or other evidence that he treats the IC as an IC and not an employee, and, importantly did not council the IC newbie to pay quarterly taxes and keep good records.
I have on several occasions seen appraisers who do not keep auto records, have no idea how many miles they drive in the course of business; pay cash for copies at the courthouse, buy supplies etc. cash or undifferentiated with other purchases at Wal-Mart on a credit card, and otherwise underreport their expenses by bunches. Even when they do report it, they often lack proper documentation.