Hi Quoll and Welcome to ROG.
If the pins were bent then I would say there is still hope as I have repaired a board with bent pins using a magnifier and tooth pick, but as the pins are broken off then unfortunately you have a dead board, unless you can have the CPU socket replaced. (doubtful).
The moral to your story is, When selling second hand MBs, don't offer Warranty and no returns, You should have demonstrated that the MB was functional prior to sale. A hard lesson learned.
We owe our existence to the scum of the earth, Cyanobacteria
My System Specs:
MB:ASUS ROG Crosshair VII Hero/WiFi GPU:EVGA GTX 1080 sc PSU:Corsair AX-1200i
CPU:AMD R7 2700X Cooler: Corsair Hydro H115i Case: Corsair Carbide 780t
Memory:G.Skill TridentZ F4-3200C14D-16GTZR SSD:Samsung 500GB 960 EVO M.2
[/HR]