Directly to the point of legality, if you provide value to a company, you need to be paid. Period. It has nothing to do with whether you can afford it or whether they will rescind the offer. If you applied to a job that offered you $1.50 an hour, you would not legally be allowed to accept those terms. If, in this case, you are offered $0.00 an hour with an undefined commission, you are still not legally allowed to accept those terms.
On the other side, if the commission is paid based on a defined set of parameters and backed by a minimum wage, it’s legal, and the only other question is whether you can afford to live on that. For a little while before my senior year, I had an “internship” with no pay except commission, and I was so desperate to have an internship that I accepted it. Now, I made decent money, but it was by no means an internship - it was a straight sales job and, after some further research, it was even listed as such on job posting websites! Same role, same company, different description. After realizing I was getting no legitimate experience, I quit and went back to waiting tables.
If a company refuses to pay you for providing value, then it is not a good opportunity. There is no ambiguity here. If you fear an offer being rescinded because you ask for the company to honor your legal rights, there is a problem here. The term “internship” is completely irrelevant unless you truly are adding absolutely no value whatsoever and the company is contributing to your education in a meaningful way (“experience” doesn’t cut it). If you do a single task that could add value to the company, then you are an employee who needs to be paid.
Also, if you are terminated or your offer is rescinded because you requested the company honor your legal rights, you have the right to sue for damages, which would give you plenty of experience in an area you never even thought of! hehe