And I am totally guilty of saying it myself! I'm going to check my words a lot more. In this case, it was assumed I knew something because anyone in that industry would know it- totally logical. Except I am not in that industry. Most of their clients aren't. They need to take a step back and remember that most people only have occasion to deal with them a few times in their lives and things aren't common knowledge. Own that you need to be the expert and risk telling people too much vs assuming they know a lot. Grrr. sorry for the vagueness of this particular situation but still holds that if you hold any of the blame, don't say, "I'm sorry you misunderstood." Own it and say, "I'm sorry for the misunderstanding. I really should have been more clear. I will remember that." (Which is what I think I usually say and then I do go forward and tighten up future communication- I'm always willing to hear and improve!)