If the price of grain had fallen, the Soviet Union would have purchased it from other countries at market rates. Only after they had exhausted other countries' grain surpluses would they have bought from the US.
The GP is talking about prices falling after, not before, the purchase.
I think the point is that the market rate was "unfair" (depending on your definition of fairness), as it was based on massively assymetric information.
Re:Great Grain Robbery (1972)
by londons_explore on Sunday April 26, 2020 @12:11PM
(#22988133)
Presumably there could have been asymmetry in the other direction too? Perhaps the americans knew they were in for a bumper wheat crop, and thought they'd lock in the price now before prices fell?
It appears the price was set based on market rates on the day the deal was done. In effect, the USA just sold all the grain on that day, more than they actually had, not on the actual day of delivery. They just issued a futures contract.
Had the price of grain fallen on world markets, the soviets would have lost out.