Is it appropriate to move into the Bargaining Stage?
The majority of Go/No-Go decisions are made at this point in the Exchange Stage and early on in Preparation when you find information that is a "deal killer". The remainder of Go/No-go decisions are made in the Bargaining Stage.
What you don't want is to reach the Conclude Stage and have to execute your BATNAs. It happens occasionally when you have been deceived about the other party's interests, intentions or commitment, but is rare in collaborative negotiations.