This simultaneous match of needs is rare. A person wanting to exchange his goods for someone else's must find someone who wants exactly what he has and has exactly what he wants.

Determining exchange ratios (e.g., how much wheat for one kilogram of rice) is difficult and often arbitrary, potentially causing unfairness. This problem becomes immense in a modern economy with millions of goods.

Three sub-problems: (1) Borrowers may struggle to provide goods of the same quality at repayment time. (2) Disputes can arise over which specific commodity should be used for repayment. (3) The value of the commodity to be repaid might change over time.

Two sub-problems: (1) Many goods (like food) are perishable and lose quality over time. (2) Storing goods requires significant space, time, and effort.