Employment Law Questions? Ask an Employment Lawyer.
Yes, a person can be commissioned and W-2, even if they are commission only. A person can also be a contractor and just commission, but being paid W-2 doesn't mean that you can't be full commission.
If he was promised a certain hourly rate though, until they told him differently he technically should have gotten that rate. That would mean that he is technically owed at least that first week or two when he thought he was getting both. He could make a complaint called 'wage claim' to the state Department of Labor if he wished. This is a protected complaint.
As for his being available, that's called "on call" time. He is only legally paid for time that he actually works, not for time that he is just on call. If he is actually working or required to be at a specific location during the time, then yes he should be getting overtime and should report the matter to the state Department of Labor.
Finally, concerning his taxes, they may be overtaxing him based on some error or incorrect entry on his W2 or their input of what he put down. He can ask them about it, but ultimately you'll get it back when you file your taxes.
If you have further questions, please raise them here. Your request for a phone call couldn't be honored due to your payment not clearing.
To address your additional questions in the other thread, he should file a complaint with the DOL for what appear to be wage and hour violations. Travel from job to job after the start of the day is paid time.