It's not two different approaches. You missunderstood my post. Telling a customer that they are good enough to use Professional quality materials in no way insults the customer. Especially if you inform them of how good their art is FIRST. I'm sorry if I sounded like I was insulting the customer's intellegence, I would never want to insult a customer... it's a good way of loosing them.
I just didn't think that I would have to spell out an entire conversation.
An examlpe of how I might handle the situation:
me: Here you go Mrs. Jones. Your painting is really beutifull. I see some really good techniques here. Are you using Bob Ross's books?
Mrs. Jones: Oh, thanks. No, I 've been taking classes at the local College.
me: May I ask why you used Canvas paper, instead of a stretched canvas?
Mrs. Jones: That is what we were using in class. Is there a difference?
me: Well, I think you are ready to try using some more professional quality supplies. You will be surprised how much easier painting gets when you upgrade your supplies. I look forward to seeing your first painting on canvas.
Honestly, that was close to a real conversation that I had with a customer of mine. She switched to canvas, and 1 year later was doing paintings for consignment. She did photo realism portraits.
A few weeks after that conversation with her, she thanked me for the confidence that I had in her. She knew that she was using practice materials, but was afraid to move on to the more expensive supplies because she didn't feel she was ready. When she switched to better brushes, paint and canvases, her paintings got MUCH better.
She once said that if I had not encuraged her to move on to better quality, she might never have become a portrait painter.