Or people could just stop buying Mars bars and other ultra-processed foods if they feel they are overpriced which would force corporations to adjust their policies. Mars, Nestle, McDonalds etc. will continue increasing prices as long as people keep buying regardless of how much they complain.

The pricing of normal raw food products, produce etc. is generally quite transparent.

Unfortunately, "external regulators" are both human, and subject to the self-serving whims of the power-hungry politicians.

Plus, nowadays, a "justice" system which might well decide that Badguys Inc. has a First Amendment Right to label and sell 10 1/2 oz. of inspection-failing mystery meat as "1 Pound Pure Prime Beef".