15% discount codes: using other people's

I don't have access to employee, upgrade, or any other discounts. But sometimes I see people offering their discounts, like here: https://old.reddit.com/r/sonos/comments/11nb118/upgrade_credit_trade 

I've got Champagne tastes on a basic beer budget, racing along on the hedonic treadmill (google it). I now have two Ones and a Roam, and I'm looking to obtain a Sub Mini and another Roam, preferably with a 15% discount. Is there anything I need to be particularly cautious of in using someone else's discount?