I know you believe it to be legit....however, in my 35 plus yrs sourcing true nigra I don't remember any that had ever been completely waxed like that. Not saying it doesn't happen, just don't remember seeing any. As a rule of thumb I have generally shied from wood like that. Too many unknowns and hidden stuff under the wax.
The only true way to tell is what Ssonerai posted and probably needs to be done in a lab.
The fact that you stated it came from ebay is an eye opener for me. In all my years buying wood, I learned ebay was the biggest scammer hangout for trying to sell things that weren't really things.
However, if you feel it is what is and get it for a price you feel comfortable with, why not.
Spruceana can smell just like fresh cut nigra with that sweet bubblegum smell.
Good luck with your find.