To sell a product or service to someone at the same or close to what the product or service will cost you. Hence the person that you are selling to is being given a substantial discount on the normal price. As the term "[mates] rates" suggests this level of discount is usually only given to [mates], or friends, of the person selling the product or service.\r\n\r\n\n> Bob: "Hey Johnno, how much did you pay for that computer?"\n> John: "Got it real cheap mate. Trev sold it to me at mates rates."\n