In the commodities market you can sell what you do not have, as long as you have it to satisfy the deal by the end of the market day. And remember, NOBODY in this room wanted Orange Juice at the end of the day, merely the MONEY that changes hands.
Billy Ray is delaying the purchase of the Frozen Concentrated Orange Juice because they are in a market of rapidly declining prices. This is because the crop report noted that there would be no shortage, and no shortage means that everyone's need for orange juice will be satisfied. In a capital market, satisfaction all around means prices stabilize or decline. A true shortage would have caused demand and prices to go up.
Dan Aykroyd and Eddie Murphy gave the impression that the market would be constricted (without saying so, I believe, just hinting). This caused the Duke Brothers to really cause the frenzy (because of course, they always made money with Winthorpe, and they had an insider report that said there would be a shortage - a clear impetus to try to corner the market). They caused a false demand to force the price higher in the breaking hour of the market. Winthorpe and Valentine sold what they did not have, merely a promise to satisfy the deal for Frozen Concentrate by the end of the day for a high price (because they had falsified the insider report - thus knowing the prices would be low). They sold high before they bought low. Every chit in Eddie's hand was for a commitment to sell a certain amount of FCOJ for the high price by the end of the market day, and as they slowed the buying, the price dropped. They merely had to keep up with the desperation of the losers (those that bought high earlier and would be stuck with the ORANGE JUICE they paid too much for) while the price continued to decline.
Number of Units Sold early has to equal Number of Units Bought now. Each difference in Sold High minus Bought Low was pure Profit.
Commodities Market is not for the faint of heart; sometimes the spread per commodity unit is in mere cents, with a fortune won or lost pennies by per deal made hundreds of times a day.