Drop it back off with them. I would notify them immediately because it could be a bad pump in which case the customer selling it should not get paid and once they pay him it will be harder to get a refund. Let them know, even just by phone but do it ASAP, drop it off and I will thoroughly go over it. It could be something simple like a parts misalignment but it could be something serious from the pump being allowed to run dry for a very long time. Once they know they can not pay until the issue is resolved so you can get a refund if it is bad. Sometimes that is a problem with consignments- dishonest people passing off broken stuff but I know they don't give anyone a second chance if they do that. I lean toward the idea it is a simple mechanical problem so don't panic but it could be more.
