Partial refund? What? around $80 on a 6-700$ piece? Have they replaced any damaged items for anyone? I don't think so. That's what they should be doing. Even the full refund offer negates you returning a second faulty car? That's not right IMO.
You can't dictate how they run their business. They would rather sell multiple Batmobiles to multiple buyers and bank on some of them keeping it with the defects, than go through multiple Batmobiles with one buyer. If they're not making money, why even bother?
Right or wrong, it's irrelevant, but I don't know why you insist on throwing money their way and keep them in business if you're all bent out shape on their business practice.
I would contact my CC company, tell them that I am returning faulty goods for a full refund. Then re-order, and if that one is faulty do exactly the same thing again. SS do not have the right to tell you that they will only refund you once, if they are selling faulty goods, you have every right to return every single item. Over and over. When they sell you something they are entering into a contract with you to supply you with a brand new mint item. If they do not deliver on that they are breaking the contract. You could and should send the item back, order a second and return that if it's still faulty. They are just trying to cover their asses, because they know they are selling faulty goods.
It would work if (1) Sideshow hasn't already refuse your business and banned you; (2) CC hasn't already dropped you due to malicious disputes. Then maybe, just maybe you might get that perfect Batmobile. Or you could save yourself time and go straight to BBTS who is offering to inspect and ship defect-free Batmobiles.