Don't be fooled by propaganda advanced by those with a vendetta.
Artists can charge whatever they want for their signature. That's never, ever been the issue.
What they don't have the right to do is dictate what you may or may not do with that signature once it has been signed, short of drawing up a legal document...and no one's going to do that when the benefit is decidedly one-sided. And, it need not be stated that a signature is not even remotely the same as a work product. As well...charging different prices for the same service...a signature...is discrimination, whether people understand that or not. "You're charging me $30 to sign these? But...you just did the exact same thing for the guy in front of me for $20....and I don't get anything extra from you for the difference in price."
Of course you should play by their rules...but you ought to understand that a lot of these creators have been lied to by so-called "facilitators" who tell them that "people slabbing are making fat stacks of cash off your signature"...which isn't even remotely true. Of course, they tell them this, so that they can then step in and say "....and *I* can help you, to make sure you get a cut of that $$$. Just sign here, and I'll take care of everything."
Which, of course, is a conflict of interest. They're lying to creators, to convince them to charge more for CGC, so they can get a cut of that extra cost.
It's quite the swindle.