Someone who just happens to be a smooth talker shouldn't be earning more than someone else. If they actually bring more to the table, that is why they should earn more.
In a company with transparent compensation you have access to what everyone else is making so you can demonstrate you bring more value to the company than other people making $X.
I love this mindset, in my experience it's a hard problem to solve.
Smooth talkers tend to fall into a few different categories that give them a leg up in negotiations - being part of a majority (usually straight male in engineering) or narcissists. (And yes, I'm oversimplifying things here just to get my point across.)
Everyone else? Some will be able to advocate for themselves, but others (especially under-represented groups) can easily downplay their worth. I've seen multiple times when women especially are trying to please the hiring manager/company and 'be flexible' in what they take. Other times it's from people outside of the U.S. where cultural expectations are different. To fix this we need people to have enough self-worth/self-esteem/trust to push on what they are worth and/or the company needs to act as an advocate on behalf of the employee. I've seen both be pretty tricky to figure out over the years.
But it helps, as not only do you know what other people are making but they'd know what you're making. So people who manage to talk their way into some extra bucks on the way in, well now their coworkers know. And if that person isn't performing at a higher level, they'll start complaining.
And then yes, there are problems with the above. But my larger point is this puts more information in the hands of more employees, which can only be a good thing. The set of employees it hurts are the one set of employees who I think shouldn't be getting ahead in the first place.