Viridian's advice is right on: calmly contact the dealer and explain what you've learned and request a full refund with return shipping costs. Don't get sarcastic or accusatory. If dealer refuses that solution, request he pay for shipment to distributor, testing, and any repairs that are necessary. I'm sure he'll refuse that solution. Any reputable dealer would accept a return and give a full refund, given the circumstances. I'd even expect a private party seller to accept a return and refund in these circumstances, because he shouldn't have shipped the table without learning and undertaking the correct shipping procedures. I have learned from my own experience with a Sumiko Wood Project that shipping turntables is extremely hazardous, no matter who undertakes to do it.
Good luck!
Good luck!