At least 20 lashes IF it can be proven. MORE than 20 lashes...a multiple of the difference between what they paid and the market price at the time of the trade souunds about right. The problem is with that IF. But if that IF has the same quality of proof as has been offered up to show that there are X millions of naked short shares in the hands of ne'er-do-wells then the extent of the described problem is equally imaginary.
I'm a little surprised to hear that "For market makers to snatch a stop loss 20-30% under the market" isn't already illegal. Are you sure that it's not?
“I have had a wonderful time but this wasn't it.” ..........Groucho