So the edge from being net short vol would come from how you manage the risk when selling vol. And that would come down to your option pricing model or some strategy around playing around with the vol curve.
Yeah, as with everything that is traded, option prices and thus vol is determined via supply/demand. So let's say an institution comes in and is looking to hedge their portfolio by buying deep otm puts. If they buy enough then those prices and thus vol will be overpriced, so then it would make sense to sell them the deep otm puts and then buy some other otm puts that aren't subject to the same demand pressure thus hedging off some of the exposure. You'll probably see the prices mean revert and then that's where your profit comes from.
So the hard part is determining when it's demand that is distorting the curve and also you'll probably want to dynamically hedge the position if it's big enough which is tricky.
And on that note most if not all short term mean reversion strategies are based on that.. so the edge is just determining when it's non-informed trading that is causing a demand/supply imbalance.
For about 4 years I used to sell vol on the Australian SP 200 futures contract and would dynamically hedge sometimes against SPX vol. Realized an 87% gain over the period (nearly 100% of starting capital). But had a 50% and 20% drawdown and an overall 2.0 sharpe. And i didn't have an edge, I'd blindly sell otm vol and buy atm vol and then would dynamically hedge off exposures i wasn't happy with (bet was pretty much that realized vol would be higher than atm, but lower than otm). So I made money cause someone was literally paying me a premium for assuming risk they didn't want. But not to be confused with an edge per say.
