Sorry to intrude, but I assume this is kinda what your tires looked like when you received them:
There is no way you or a shop wouldn't notice that kind of damage and bubbles. And absolutely no way a shop could mount those tires and still not have seen it until finished.
The seller is a good guy and to me it seems he's tried his best to resolve this situation.
You also say that your shop can vouch under oath for those bubbles being there before mounting the tires? That's interesting... either they knew that the bubbles were there and then they should have called you immediately and not mounted the tires. Or they didn't know and then what you are saying is that your tire shop is willing to lie under oath... in which case I wouldn't trust their word for anything anymore
Sorry to bust in like this...