Thank you for the response, Mathieu Roy!
I see exactly where you’re coming from and I relate a lot to it. I have ghostwritten articles for things I’m not personally using or believe as well, but I think since the research is done and the as long as the product does what it claims, I still don’t think of it as deceitful. The product does what I wrote it does, I just don’t use it. An example for me might be an article about how to best train your puppy. I don’t have a puppy, but I still understand and had done research on the most well-regarded ways to do so.
As we have writing skills and we are often writing for people and companies who cannot seem to be able to articulate what they want, I don’t think it is lying to put their words in a way that makes more sense or is more compelling.
Same with ghostwriting books. Many people have a story to tell but don’t know HOW to tell it in a way that makes the most sense.