Also there was tape on the PCB in multiple places like he couldn't get the springs to stay where they needed to be.
If he didnt disclose all of this (the opening of the board, taping down the rubber dome sheet) - I'd ask for a full refund regardless since he wasn't up-front that he'd hacked on the keyboard. That should have been made very clear. Heck, I'd ask for a refund since the ESC doesn't work. If he says 'no', open a paypal dispute.
ProTip: in the future take a screenshot of the sales post on MM for future reference. 99.9% of deals go through without problems, but better to be safe if you turn out to be the .01%
The original selling post was on Reddit but it was removed since he put it on /mm but didn't have a price so it was removed
If it was just removed by the mods, it may still show on his user page. Go to the users home page (e.g. /u/<username>) and hit the submissions button, it may still show up there unless they deleted it on their own.