renton
Always check what you buy mate including taking the rear shock off and going over the frame inch buy inch. Same rule applies for a whole bike.
Most used frames or whole bikes need a lot of work, blown shocks, ruined bearings, bent mech hangers, brakes that need new pads or rotors, forks that need serviced. Ask the person when the bikes or parts where last serviced and then varify what they say when you see the bike.
I think you would be better of buying a frame from ebay, that way you have time to check it out.
Sorry to hear about your new ride, I get a lot of hassle with the frames I sell so I tend to take the side of the buyer. If the frame is described as like new, I would expect it to be with very little ware and everything working.
You should chalk it up to experience and simply learn from it and get some new pads to stop further cable rub and cover the existing rub up.
Ridefree!