That pump deal is awfully cheap.
I've ruined a pump or 2, so a couple of things I'd check. First, make the seller sets up and runs water through the pump. It looks like it has a Honda, or a Honda clone, so I'd check the oil. These engines are built to run for hours, but the oil gets nasty PDQ. If the oil's low, or looks like black toothpaste, then it may not have had the regular maintenance it needed.
When pumping, the outlet hose should be fairly rigid. If you see multiple slow waves in the hose, then it may have a worn out pump. I would also cap the outlet and check for hose leaks. Either of those issues could wind up costing you more than the pump itself.
