I have recently accepted a free-lance job to typeset a book in LaTeX for a publisher. I'm not a professional graphic designer, but I have been working with this tool for a long time now. Now I even realize I charged a fraction of the market price for such a job (why should I earn less than someone who just uses a different tool?), but that's not really the main issue.

The client has asked me over and over for changes, not only design but also copy-editing work, some of which I declined to do.

Now the job is practically done (all that is left is to include the ISBN number), and after serious delays to receive my pay, they still want me to send not only the .pdf (whose final version I had already sent) but also the source file.

I'm afraid they'll either mess up with my job (which took me quite some time to accomplish in detail) or take my design/programming and send to someone else who'll do the easy job of "adding stuff" (or even make it a template for future books).

Should I really send them this source file? If yes, should I charge more for this?