If they are telling you not packaged according to their guidelines, then I don't think they are offering you anything regarding the damages. Sorry.
As for guidelines, well, I'm not sure about those. But I will say this. If the box has no square corners or edges, you might then see how much force a package can experience. If the box is caved in or the damage, if it was photographed by the buyer to document what happened to it, can be correlated to external damage, you can then see what may have damaged the receiver.
IME, with very heavy items like a receiver, the issue is the weight or mass punching into and through packing material, sharp edges, corners, and all knobs, switches, controls, and glass being exposed and vulnerable.
Sorry to say, foam padding, unless at least 2-3 inches thick and very dense (cannot compress to 1/2 the thickness), is a poor material. Most foams will compress easily and allow force to penetrate inside. Bubble wrap, while really good for lightweight items (like up to 20 pounds), can be defeated by repeated bumps and falls where the object itself can pop the bubbles and allow for more movement, making it worse. Any movement inside the box can be hazardous. Finally, without a strong double box or double wall box, the box itself is not help in protecting against shipping damage. In some cases, its is literally just an outer cardboard or corrugated outer wrapping.
At that point, if packed with the above materials, your box should have been at least 4 inches larger in all dimensions around the receiver with literally tape holding all surfaces closed tightly around literally bulging contents. If you lifted the box over your head (almost 6 feet) and then threw it down onto the sidewalk, do you think it would survive, especially with an angled or corner hit? And then if you did that at least 5-6 times, would the receiver still be undamaged, and would the packing material used still provide for no movement inside the package while remaining intact?
I'm sure you felt your package was packed well enough, otherwise you wouldn't have sent it out. Its just that all the carriers will do exactly the above in "treating" your package to their system. Repeatedly. If your package gets gored or run over by a forklift, gets dropped off a loading dock, falls from a conveyor 6-8 feet off the ground, the last deliveryman, drops it from his shoulder onto a corner to the buyers concrete stoop, that's what we all have to pack for.
Here's the guidelines I can find for UPS:
http://www.ups.com/content/us/en/re...guidelines.html#Guidelines+for+Good+Packaging
http://www.ups.com/content/us/en/resources/ship/packaging/guidelines/how_to.html
Frankly, given the size and weight of our larger pieces of gear, and their fragility, I'm not sure any of them can reliably be packaged and survive without heroic packaging. Even factory packaging, sometimes meant primarily for bulk pallet shipping, isn't enough.
Its just that the shipping systems are geared towards speed, not safety so much.
Sorry, I've been there and learned some of these lessons bitterly.
