"I don't know..." is not a real qualification. Qualifying things also means working at doing proper qualifications. "I read a comparison of library X and Y a while ago that stated (qualification) library X is bloated to library Y, so we should investigate that before making a decision as too which one to use"

It is a great point that people don't qualify because it makes them sound less confident, and people that sound more confident end up being more convincing to most people. So there is a cultural problem there (hopefully confidence does not sway a scientific group).

Cultural problems are tough- to maintain your stance you have to try to change the culture (sometimes impossible) or move to a different culture. But you can change the culture a little by asking "where did you read that?", or "so you have used/did that yourself?". Obviously you have to do this in a way that doesn't annoy.

You have to work at finding the middle road between qualifying and giving an impression of relative confidence.

Let me qualify this by saying these are just what comes to my mind on this issue. I would very much appreciate the pragmatic advice of others on this concept.