Disclosure is required in the def-14a and in the footnotes. Common examples are leasing property from a founder, buying services from a director's firm, or selling to an affiliate at a price nobody else would get.
Most are small and harmless. The concern is pattern and scale: a company routing meaningful revenue or costs through insider-controlled entities has weakened the link between reported results and independent economics.
Example: Northwind Tools discloses $3.2M of annual rent paid to a partnership controlled by its founding family for two distribution centres, on terms an independent valuer confirmed as market rate.
Related: def-14a, footnotes, off-balance-sheet, earnings-quality, form-10-k