I was actually the seller. I was assured by the UPS Store in my area that I'd packed it fine but lost the damage claim (even though I bought insurance!). Sigh. It's pretty upsetting, but what I wasn't aware of is that by using the UPS Store I waived the right to handle damage claims myself. The UPS Store submitted a claim and it was denied; UPS corporate won't let me appeal it since I'm not the "primary shipper."
So why let an otherwise perfectly good Mac Pro go to waste? I figured I could fix it back up and make the best of the situation