In a commission-only sales position, can an employer require employees to clock in-and-out and work set hours with no hourly compensation?

If you are an independent contractor, then the employer probably cannnot set a working schedule for you. (The reason I say "probably" is that if the nature of the work is such that it MUST be performed during a set time, then that's reasonable.) Also, the employer cannot make you clock in and out, even if there is an appropriate time to perform the work. Exercising that degree of control over when someone does a job is appropriate for an employee, not an independent contractor.

Also, whether you are an independent contractor or an employee does not depend on employer whim--it's based on your relationship to the business, and as long as that relationship does not change, the employer cannot reclassify you at will. Either you are an independent contractor or not.

If you are an employee, then you are subject to the Fair Labor Standards Act and the employer must pay you commensurately (there are special rules for commissioned employees under the act).

Also, be careful that the employer's "games"--there may be no better word--for how you are classified do not incur tax liability for you, since independent contractors and employees have very different tax obligations.

I think you want to get this resolved; be classified as whichever is appropriate and then work in that fashion. The back-and-forth switching is improper and can cause problems.