Photographed group shots of a family of 8 who wanted about 10 different combinations of subjects. When they saw the online proofs, they asked if I could change out a head from one proof to another. Also could I make the lady look less "chunky". Went ahead and made a proof with the head change while explaining that this was beyond the re-touching fee that I charge for the pictures they select. Also did some quick liquify reshaping of the lady. Since it's part of a larger order I planned to charge them a nominal amount if they chose that photograph, but didn't communicate the specific additional cost, or that I really cannot guarantee an outcome as good as the one I did. ...my mistake.
After seeing the proof, I got an email requesting an additional 9 "head swaps" on four photographs. I consider myself reasonably competent with photoshop, but it's not until I get into making changes like this that I can see whether it's going to take me 30 mins, an hour or if it's going to look natural when I'm done.
How much would you quote for this, and what if I don't think the result works?