Sure!
If you give me a commission to write a programme for you , "AND" want the source code as well as the exe file it will be at a different price.

But to give completely away the results of, sometimes a few months work to someone, to do with it as they please for a NORMAL fee is insane.

If you gave me the source code to a good working programme, I could dress up the interface and make some changes so that not even the originator would easily recognise it .
And I could market it as my own!!

I would not do it of course, and I don't think you would either but it could be easy.
Cheers.