Exactly Wolf-Hound. :)
I think grooming is a great bonding time for dogs and their owners. It's also a great training session and keeps the owner aware of their dog's condition to easily spot things that might be wrong. I will always encourage an owner to learn to do some or all of it if they can.
Many will try, and decide it's not for them.
Many will try and be able to accomplish a groom that they know it's professional quality, but is good enough.
My own Dad and Stepmom groom their own dog. They are snow birds and during much of the year are on the road. They can not imagine just dropping her off to a stranger and leaving her there. Maybe once in the summer when they are back home, I'll do her. It's mostly to do the things they find difficult. Yesterday while over there for a family dinner, I clipped her tummy, rear, and below her eyes. I'm comfortable enough with the clippers to do it as short as it should be done. :)
It took some trial and error for them. They didn't take my initial advice on equipment and instead bought some discount store clippers. One grooming and they asked me for a list of what they should be using. With professional tools, they do an alright job. I've seen worse coming out of some grooming shops. They are happy with how she looks and their minds are at ease not having to worry about a stranger working on her.
I would be unhappy if I got a cold call wanting to come in and watch me groom their dog one time to teach them, without any thought of compensation, or even worse just asking if they could come watch me groom any dog so they could learn.
I don't mind helping out a new client, depending on how they ask, the reason for asking, and the amount of respect they show when talking to me about it. The woman with the Standard Schnauzer was very honest in that they would only be here a few more months and she was hoping to have me set the proper lines so she could follow them on her own. She was also honest in that she's done quite a bit of stripping on him herself, but wasn't sure where to go from what she had done, to make him look right. She was honest that she has someone else groom her Giant Schnauzer, and she's very happy with her work, she just doesn't do handstripping for this dog. I liked that. I set her up on a morning when I had no one else coming in, and will have her stay and we'll work on him together. She was thrilled and I was happy to help her out.