Many images can benefit from retouching, this could be removing dust or marks from scanned originals, or even people and objects.
Anything which detracts attention from the main element of the image is worth considering for removal. I will suggest any improvments that I could make when I see your image
Simple and quick jobs would be offered free as part of my normal printing service, for more ambitious jobs I would give you a price at the outset based on £30/hr
This is an increasingly popular service. If an image has been damaged in an unimportant area... eg clouds or sky (eg a corner creased or even torn off completely) this could be a simple to fix and probably free of charge.
At the other end of the scale, if the damage involves important areas or lots of detail there may be hours of computer work involved in the repair. Eyes and faces are usually the most difficult and time consuming.
I usually scan the original, which you can take away with you, then work at high magnification on a computer, it is not particularly difficult just time consuming.
As a guide to cost I would suggest;
1/2 hour (£15.00) easy jobs.
1 hour (£30.00) more typical jobs.
2+ hours (£60.00+) lots of detail.
I will agree the cost with you before under-taking the work ........ and if you don't like the result I will return your originals with no charge.
Seems fair ?