Kautilya's Arthashastra 4.2.24

4.2.24

kretṛvikretror antarapatitam ādāyād anyad bhavati //

It is the duty of the trader to calculate the daily earnings of middlemen and to fix that amount on which they are authorised to live; for whatever income falls between sellers and purchasers (i.e., brokerage) is different from profit.