Remember, that no matter what you do, where you go, what you buy or sell, ethics is a big part of it. If you plan on doing an honest business, then disclosure is the key. TELL THEM what you need to tell them and not what they might want to hear.
I always say to my clients, that I am very up-front. If I do not agree with them, I will say so. Being a Realtor is getting harder and harder each year. With over a decade and a half under my wings, and being Italian, I learned since childhood, that YOU TELL IT LIKE IT IS.
So, my best advice to all, is be honest. No matter how hard it is, how much you might loose that sale, or what the stakes are, TELL THEM what you need to tell them. On the long run, they always come back!