This is another question I am often asked. The answer is in most case almost certainly especially if the subject is female.
I was talking to a wedding photographer one time and I asked the same question. He told me that if he doesn’t re-touch he gets far less final sales.
The key is not to do too much. Don’t make a sixty year old look like a 30 year old but taking 5 or ten years off will almost certainly get you a sale.
You saw some images of Annie Moya yesterday. At 26 she has beautiful skin and to skin smooth her until she looks like a plastic mannequin would be a sin. She had a few small spots on her chin, you poor girls must hate those hormones doing that to you, and so a little spot removing with the clone tool is all that is needed.
You will also find a few more examples here.