Go to SEC.gov and read the many litigation releases and the like. U.S. trading rules (But not laws) don't allow shorting certain stocks but I think Canadians and others can do it if shares can be borrowed.
Shorting any stock is risky; I've never shorted a stock. Shorting creates short term gains, not LT capital gains that are tax-favored. But if you're an insider with a garbage stock and control it, especially the dilution, you can short your own company with almost total confidence. From what you've posted, MMRF looks clean on that score right now.
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