I'd question how blind the auction is when Sky and BT ended up paying the exact same amount per game in the last rights sale

The League doesn't have to take the highest bid though and you're right, Amazon paid less than the reserve for the package they bought. I'll dig out an article when I have a moment but it was speculated in a number of reports that the PL were willing to sell those cheaper packages for less to Amazon (which turned out to happen) because they wanted them to get a taste for the PL in preparation for future sales.