Market is fat . Buyer and seller transaction-frequency and identity is unimportant. Standardized, durable or non-durable, simple or complex goods and services. Uncertainty is small or high, and few measurement problems. Small asset specificity.
Market is thin .
Buyer and seller transact seldom or often. Identity is ex post important. Customized often complex, durable good and services. Medium to high asset specificity. Employer and employee transact frequent on bundles of services.