While people persuade and manipulate in order to get others to do what they want, persuasion is more honest. When you persuade someone, you are simply presenting your product, service or argument in the best possible light. You don't need to lie, omit details or intimidate the other person. Rather, persuasion is truthful -- the facts presented are real. It is giving people information they did not previously have in a clear, logical manner in order to convince them by informing them rather than manipulating them.
Manipulation is about getting people to do what you want through subversive manners that lack truth. So where someone may persuade someone else by giving them facts, a manipulator may make up or imply facts. Manipulators don't care how they get their result as long as they get it, which means they are less concerned with the facts and integrity of their process.
Persuasion uses facts, while manipulation relies on emotions. This is because emotions are less concrete and harder to pin down than facts are. If, for example, one car gets 20 percent better mileage than another, a salesman would have to use manipulation in order to sell the second car to a financially discerning customer. Rather than focus on the raw facts (the mileage), the salesman may manipulate the customer by selling the second car in terms of how it makes the prospective buyer feel.
Bob Burg, a successful salesman, speaker and writer, describes persuasion and manipulation in terms of what the persuader (or manipulator) wants. A persuader will serve the person he is persuading; he will sell a product or service that he genuinely believes will add value to his customer's business or life. A manipulator, on the other hand, focuses solely on himself. He is not serving another person but rather targeting someone for his own ends. This is the key difference between persuading and manipulating.