I agree with what has been said so far. Putting yourself in the defensive position right away is a bad move, much like in chess, where the goal is to always be on the offensive, or you will never win the game! Getting more details is the best way to go, because i have often found that they don't even know the specifics of the bad things in the first place (unless it was an actual personal experience). Otherwise it is just what they have heard, and "I heard" is probably the most quoted individual out there (at least that's what I heard....) :)
At the end of the day, YOU are the one that is going to turn around the negative feelings. Your demeanor, your ability to present and handle their personal issues is going to be key. Your service you give to them is going to be the best way to counter any negative thoughts about what they may have heard or thought in the past. It goes back to the big principle of positioning yourself in a way that they can trust you and know that even if they hear negative elsewhere, they know the truth because they are experiencing it with you right now. You may want to ask them directly if what they have experienced so far with you has led them to believe what they may have heard in the past. (Plus, are they right? If so, then this may be something you need to address internally right away, but don't jump to any conclusions with knowing all the facts first).
This is a challenge I face as a recruiter everyday as our indsutry does not have the greatest of backgrounds, so when there is an organization such as the one I am involved with that is good, it is a daily challenge to counter the negativity that has existed for quite some time. I am interviewing people everyday and have them sitting in my office or on the phone when those issues come up. More often than not, I have to fight the little battles everyday to "brand" my organization in a different way to dissipate the dark cloud that still exists. After awhile, you have so many more people on your side, that you can gather a good group of testimonials that you can use as an arsenal to share with those you are selling to so that they can get specific feedback from others and not just from you. This builds tremendous credibility to address this issue, and it gives you more reasons to thank the clients you are already working with to continue building on those relationships.
Steven J Smith, PHR
http://yourutahsoi.wordpress.com