Good question. I don't know what they can do. Going after the pump groups would be difficult. Yes, they could try to single out the leaders and sue them for securities manipulation, but there're tons of these groups, and most followers would just switch to a new one.
I think some of the volume--especially in issues that used to be Grey and are now "Expert"--may come from the toxic funders. When the SEC suspends a stock the toxic funders have lent to, volume usually drops quickly after it reopens on the Greys. The lenders have no way to dump the rest of the stock they may have.
But now we have the Expert Market, thanks to OTC Markets. Since it features electronic execution, the toxic lenders find it much easier to dump whatever shares they're stuck with. And that kind of volume prompts others to buy.
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