I don't offer retouching for other photographers, the time, talent and effort it takes to create my art would be cost prohibitive for a photographer looking at me to retouch their work. I will, however, retouch a clients image from a session with a different photographer.
You will have to get the photographer's permission to allow me to manipulate and change the image, and I will need a copy of a signed agreement (that I will provide), to ensure that the image maker is ok with this arrangement.
Pricing on retouching does not differ from my print/product menu.
The requirements for retouching require the original, unedited, RAW file from the photographer.