I have a great idea for a business. I'll invite people to send me money. For every dollar they send me, I'll send them a receipt saying "Thanks for sending me your dollar. You can have your dollar back whenever you like subject to the following condition: you don't really have any right to have it back. And I promise I'll put it in my bank account and keep it there until I decide not to anymore." And people could use my thank-you notes as money!
Would this be a scam? No it wouldn't. A scam is, by definition, a deception; a scheme based on dishonesty and fraud, and I'm being completely candid about my intentions.