What a great post! Fab information, thank you for sharing. I have only had one business so far and it's going back to when the pack first came out so I can't remember accurately enough to give proper info, but here's what I can remember.
I had a sim making flower arrangements to sell and her live-in daughter-in-law also mentored customers on painting. They had a greenhouse where customers could go and garden and there was a board in the greenhouse too where my main sim would give flower arrangement and gardening classes. If I remember rightly, most things went really well. Customers bought flower arrangements, they attended any classes which were run and they used the paint boards and the flower arranging tables appropriately, though I cannot remember if they finished their projects. Both of my sims did one-on-one mentoring for extra fees - though, I think, sometimes the sim being mentored would get bored and go away before paying the fee.