One of the professors asked me if I could help with the page numbering in his student's dissertation. I said sure, of course. The student sent me the document and I added the page numbers, and fixed the margins and a few other egregious errors. I also offered some unsolicited advice about the formatting, especially the headings and ToC. He asked if I could help with that and I said okay, though now it is getting to be more than a quick favor.
I sent him the dissertation guidelines that another professor had given me (why hasn't he received this?) After a few more emails, he sent me a list of the new headings, asking me to make the changes and then generate the ToC. I said he needed to make the changes himself, and then I would generate the ToC (at this point, I also said I normally get paid for this type of editing work).
So he sends me the revised document, but he uses his original instead of the version I had corrected for him (free of charge!) He actually said "add what you did before" - so cavalier. Just redo all the work I did for nothing. Unbelievable level of entitlement and lack of appreciation.
I learned my lesson - the next time someone asks for editing help as a "favor," I will negotiate for payment, regardless of how minor the help they appear to need.
ADDENDUM
To be fair to this student, he offered to compensate me for the help I'm providing, and asked me to review his references and citations (which are a mess, as are his tables, figures and appendices).