The oligarchs may be elected in the USA, but they're oligarchs just the same. In fact, the purchaser of the groceries must value the groceries more than the purchase money. And the seller of the groceries must value the purchase money more than the groceries. Both parties have exchanged something for higher value. A women paid thousands of dollars for Elvis Presley's fingernail clippings.
All voluntary transactions take place because each party exchanges something for more value.
The trick is to understand value objectively instead of subjectively. That means we must distinguish between the actual value of something and how desirable or useful it is to us. In the car example, where I've used energy as analogous to value, there is less energy in the speed of the car than there was in the gasoline. The reason the driver accepts the loss of energy in the process is that the smaller amount of energy in the speed is more useful to him than the larger amount of energy in the gasoline. In your example, the value of the fingernail Page 2 March 1999 clippings was probably less than the value of the money the lady paid for them.