What are the rules...

Well, I have to say that this could be seen in a few different ways, since there are mostly multiple opinions in the audience whenever ATA is used. I'm not quite sure if there are any rules regarding this topic, though...
Let's see a few possibilities for the situation: 

1. The audience is allowed to discuss the answers in a constructive way, as long as there is a full agreement to the chosen answer. (If there isn't a specific certainty, the members could use the process of elimination to go for an appropriate choice.)

PROS: There are more minds working on a solution for the question and find a conclusion in the discussion.

CONS: It may take some time to find a full agreement on an answer, since ATA is usually limited (Please correct me if I am wrong here).

2. The audience shouldn't have a discussion about it, but is only allowed to rely on their own mind and pick the answer that they are most certain of. 

PROS: Having to face the task alone, the member will most likely be determined to help in some way, even if they don't know the answer.

CONS: It could be the exact opposite, with the person who is voting not being able to come to a conclusion, because they cannot figure out what the most suitable answer could be.


In my personal opinion, there are many situations which could change the result of "Ask the Audience" for the contestant. But if we would like to make a specific rule for that procedure, it could be this: The audience may discuss the answers and share opinions, as long as it is executed properly with the audience having the ability to help the contestant out.