iPad Air sold online as new: how can I be certain?
My iPad Air did not include earbuds - I don't think any iPad model has even included earbuds. 

As far as I can remember, every iPad I have bought from Apple has been received ready to turn on. If not 100% charged, then 80% charged or similar. 

iPads do not come with a big manual at all. There's a little booklet with a few "cards" that explain the buttons on the iPad - that's really all.

So all in all, none of those observations should lead you to conclude that your iPad was not new when you purchased it.

To be sure, I would go to the Apple Support site and check your warranty status with your serial number.