I suspect the likes of WinSource will end up being bag holders sooner or later - you can't buy millions of $ of stock and sit on it forever. When inventories at companies fill up, Digi-Key and the likes will start bringing parts back into stock and at market prices, not 10x. No one will want to buy from WS, etc., at 10x the price and they'll lose money even selling at cost because storage ain't free.
The way you play that game is, buy up initial stock -- that's your inventory investment, at market price more or less. When market dries up, people come to you at the inflated price. Eventually the market recovers and your inventory goes back to the same value you started with.
Thus, you need to make enough profit in the bubble, to pay back the inventory cost. Plus acquiring ongoing stock during the bubble, which won't come as cheaply, or with the same quality.
So, you plan on your excess inventory being relatively worthless, certainly no more than the baseline price was. You can sell off the excess after the crash and make back a little, presumably. But you'll need to cover the rest with enough of a bubble to be worth it. So, not like day to day inflation, or stock fluctuations, but 2x, 10x, or more price bubbles, like what we have here, it's worthwhile.
The later you start, the more expensive and volatile your inventory will be, and the harder it will be to make it back, let alone make excess profit. Obviously, it helps if you can predict the future more accurately,
like by starting one yourself. Bonus points for also starting/being the marketplace, appraisers, etc. -- in which case you make money even if the bubble doesn't kick off (albeit maybe not as much as was spent starting it up, and obviously this only works with markets that are small and scattered enough to monopolize). And, y'know, assuming you avoid the feds for these obviously illegal practices...
But that's something a bit more involved than your basic buy-low sell-high, and so I digress.
Tim