Something’s wrong in the professional speaking world and it’s paying to speak.
There’s a significant number of large scale events where many of the speakers in the lineup pay to speak on the big stage.
In and of itself, there’s nothing wrong with this. Businesses pay to get in front of people all the time. It’s basically an advertisement.
Like with other forms of hidden promotions, the problem is when it’s intransparent.
If you buy your speaking slot, say so. If you’re the organizer of such an event, say who paid to speak and who got paid by you to speak. If you’re sitting in the audience, demand transparency.
It’s a simple rule that applies to any kind of advertising.
Just be transparent!