So the way they made money is relatively simple. (Long explanation follows 🤣) these numbers are made up, but relatively accurate to the movie. The exact numbers don’t matter, just the idea behind them.

The fake crop report they gave to the Dukes stated that the orange crop would be worse than usual, which would theoretically mean that there would be fewer oranges (and subsequently less frozen concentrated OJ) and these would then be more expensive than normal. This led the Dukes to believe that they should buy all of the OJ right away, no matter what the current price was, because if this report was true they could sell the OJ in the future for even more than they purchased it. The other buyers noticed this and started following the same strategy. With everyone buying, the price spiked higher (like $150).

Now in come Billy Ray and Louis. They know these prices are insane and wildly overpriced, so they start selling at a lower price ( $125) than what the market is offering (it’s technically called “short-selling” when you don’t actually own the item itself. You are selling now with the promise to buy it back by a certain date, or to provide the item to the buyer by a certain date). They are still selling at a price that is higher than what the real value will be (because of the buying frenzy), but since they are offering it at a lower price than the market, everyone starts buying it from them, making the price start going down.

The Dukes suspect something is up and then we get the scene cut to the actual announcement: “the orange crop was not overly-damaged by the winter, and should be relatively normal.”

Everyone hears this and realizes they paid too much for their OJ. There was no reason to pay any more than normal prices, and they’ve all made an expensive mistake. They need to sell, but no one wants to buy because they all know the prices are too high. Cue Louis and Billy Ray again. They’ve already (short) sold at a higher price and now they need to actually buy the OJ to fulfill the other part of their obligation. Since everyone knows the original buying was an overpriced mistake, and no one else is buying right now, these two are able to offer lower prices and people are glad to get any money back for their mistake (if you bought at $125, it’s better to get $50 back than to get nothing and end up with OJ that’s only worth $30)

At the end of the scene, Billy Ray and Louis have pretty much “closed” all of their positions (e.g. bought back enough OJ to match what they initially sold). Even if in the end they paid $50 for OJ that is only worth $30, that’s not where they made the money. They made the money by initially selling at $125 and then buying it back at $50. The Dukes seem to not have been able to sell any of what they bought, which leaves them with a ton of OJ that is worth very little. Places like the Exchange depicted here will have credit in place for people like the Dukes so that they can just trade without having to worry about where the actual dollars come from. But at the end of the day, they still need to have a way to cover what they “borrowed”. And since they thought the OJ in the future would be worth more than any price they would pay for it today, they blew past their actual net worth and owe hundreds of millions of dollars.