No, they are deceitfully agreeing to be transparent in wages. The deception is that it's secretly to not allow people to leverage their offers or ask for more.

Where is the proof?

Is the claim also that at an auction, when people bid on something and yell out a number, they are “secretly” telling other bidders to not bid more?

Markets all over the world for thousands of years work on the basis of buyers telling sellers what they are willing to pay, and sellers telling buyers what they are willing to sell for. The whole process of a buyer and seller coming to an agreement on price is central to determining movements of supply and demand curves.

If either buyers or sellers have sufficient control to dictate prices, then that is a separate issue of there not being sufficient buyers and sellers.

But price transparency always results in a better allocation of resources and a healthier marketplace.

I think you are talking about "maxim" price though right. A car has a sticker price of 10K on the showroom floor, but nobody pays that. You negotiate down from there.

I think it would fine for companies to advertise a sticker price for a job, but nobody expects to actually earn that, you negotiate up from there.

Everything is always up for negotiation.

I know a few people who paid more than sticker price for a car in the last year.

Companies can advertise min, max, whatever. The person accepting is going to be deciding based on how good the total offer is versus somewhere else. But if a company knows which way prices are moving since they do a lot more buying of labor than an individual does of selling of labor, then the company has an advantage. Reducing this advantage helps level the playing field.

I never said what you implied. There is no agreement other than the law. I was just describing the likely outcome of the law in my opinion. AKA the deception of the law itself.