I recently received an email by a reader. Her question is a common one, and one I've dealt with: What do you tell your sources when you are writing on-spec? Do you tell them you are writing for the publication? Here was my reply:
The best way to go about this is to tell your source that you are working on-spec for XYZ Magazine and leave it at that. Most people don't mind and those who might care usually don't know what "on-spec" means.
If it turns out that your article isn't accepted, simply tell your source that the article won't be published with XYZ Magazine, afterall, but you are looking for another publisher that is well suited for the piece.
You don't have to go into detail about why the article didn't get published. Articles don't get published all the time, whether you are an expert writer or not. Publication needs change, magazines run out of money, etc, so there's no need to worry about your credibility.