They wanted to trade excess goods, in other words, unrealized profits, for something usable to them to realize the profits of their labor.
Everyone's intention is to profit, that is the reason you sell to the market.
It shouldn't be surprising when one of these parties isn't trusted by the other two...
It's essentially scalping. Do you trust the people who buy concert tickets in advance and sell them to you at a 100% markup? They're serving the exact same role in society as these market players. No one likes them for a very good reason.
One party produces oil and a second party consumes oil, but those events do not occur at the same time. A third party 'stores' the oil meanwhile and charges for it. You are welcome do it for free, I'm sure you'd be a hero to society.