Blind bidding and a brokered auction are often described as the same thing. They are close, and the difference shows up on the second round.
In a blind auction a seller receives numbers and decides alone. In a brokered process someone who knows the buyers receives the numbers first, knows which of them has room to move, and asks. A first offer is a starting position at almost every provider in this market. Whether it moves depends on whether anybody pushes it.