The CPU is all but discontinued but was retailing for about $150 before they pulled it. The MoBo is about the same $140 ish.
The issue here is trust. Do you trust the seller and do you have right of return should it not work ?
Personally I would not want to spend that much on un guaranteed second hand parts but that's just me you may feel ok doing so.
There is nothing wrong with using second hand part's heck I reuse and mix and match all my old parts to make and upgrade the family's PC's. I have been doing so for years.
The difference is that I know the parts are 100% working.