That's a tricky one! I know for me, as a demo, I end up with TONS of card fronts and then have to make them into full cards to sell them. To comply with the Angel Policy for SU!, I have to stamp them with my copyright stamp. I feel guilty about doing this as I didn't technically handstamp them, but am not going to buy the Creatively Yours stamp set just to get around it.
That said, I do sell cards I make at demo get togethers and don't feel guilty about that because I actually handstamped them. I think it is fine as you paid a fee to take that class, so the cards have become your property. Plus, if your demo is anything like me, likely she's CASEing from other people anyway!