It's a floor model. They're notorious for being way out of adjustment.
Also, It could have been dropped, or sat upon. Then again, sometimes
you just get a dud. And why it's not flat matters. Is the top not
flat or is one of the tables just sagging and correctable with shims?
If you really want to be sure, go over to woodcraft and buy the jointer
from them. They'll probably set it up for you and make sure it's flat.
And if it's not, they'll take it back and make it right. You won't
pay $280 though.