I believe truth will ultimately prevail. No system can subdue truth forever.
- The Dalai Lama
Scrum is all about truth. In waterfall, you can hide behind project estimates and big requirement documents, but not with Scrum. I've heard a number of experts say that Scrum will make your problems visible.
One tactic that I've heard with bidding for a project is to bid low and then make up for it with changes. Is that being truthful? Maybe it's the only way to get business.
I do a lot of project estimates, and I always tell people I can give an accurate estimate on the last day of the project. The further we are from that day, the less accurate my estimate is. I don't try to pretend I can finish in a certain amount of time when I know it can't be done. I've moved toward this approach as I've become more agile. I think agile is about getting away from a system that hides the truth.