Depends on the situation. I skimmed through the thread, and it seems you are working with a publisher. Like others have said, if you signed a Contract, and NDA with them. You should be fine. You can take legal action of they steal your work, at that point.
If it's someone that just says, hey can I see your .capx, then a swift "nope". Unless you are teaching a class and share your source with students, or something along those lines.
Context is everything.
Like someone else mentioned. If you need help with a particular issue, you can always recreate the issue in a small demo source file, and share that for help.