A definition of manipulation from Seth Godin.
If people know what you already know —about your product, your service, and your methods— would they still be eager to buy from you? (or vote for you 🙂)
If we use leverage and pressure to get someone to make a short-term decision that they will regret in the long run, we've manipulated them.
No regrets, no manipulation.
- Seth Godin, "Work That Matters." Interview by Kieran O'Hare. Offscreen Mag 23rd Issue