I suspect FW is right regarding the pump being a return, that the supplier shipped without removing the oil.
I would return it, simply because you are dealing with nonprofessional's, so you have no idea what the rest of the story is, including where all inside the motor portion the oil may have seeped.
Most simple rotary vane vacuum pumps have an oil fill/breather in the top, which oil flows freely out of when the pump is upside down or sideways.
Since there is nothing to keep the oil in place, the postal service and shippers typically have HAZ MAT covenants against it, which is why they oil is typically shipped separate for the excited new owner to add just prior to use and after the freight services have their way with it as a football.
The dozen or so I've purchase, had both the pump and sealed oil container heavily encased in Styrofoam, in anticipation of a rough journey in any position.
The bigger question is why the pump was returned and what use it saw before hand.
Of further concern, is that if they were professional enough to test the return for function, they would have ostensibly recognized the need to drain the oil, soooo was it tested?