All relationships are based on honesty and trust. You wouldn't want to work with someone you can't really rely on to be transparent right?...
This is so true - but what I believe what is equally important in your work life, is being honest with yourself too. So what does this mean?
How many of us have had opportunities drop out due to something we knew about but ignored, hoping it wouldn't raise it's ugly head. But as surely as night follows day - it inevitably happens. These potential issues need to addressed and plugged up front. If something needs to be fixed, fix it early and be completely honest. This is of course the right thing to do - but it also can make the opportunity much more likely to happen.
So for example, if you work in the recruitment industry and the candidate said they want a $100k salary and the client's budget is only $95k - TELL THE CLIENT, don't just hope that they will pay more. Also tell the candidate that it's is unlikely that they can pay $100k - but you will ask and let them know. And if travel is 50% but they will only do 40% - TELL THE CLIENT. In most cases, people are reasonable and can be creative to make it work. If issues arise at the end of the process, you will upset both sides - and you will be crying into your beer when you see your commission check.
So be brutally honest with yourself and proactively find problems to solve. Honesty with yourself is always the best policy :-)