I have a fairly light stance on manipulation. It's not always a bad thing and even when it is the intentions of the person need to be examined before condemning them entirely. Now obviously some people are just completely selfish and will do whatever it takes to get what they want, but it's usually more complicated than that.
I walked into work this morning and I find a note left for me imploring me to decline an exciting job elsewhere because I am really needed where I'm at. I felt guilty. The intention of the note wasn't bad. The person who wrote it is simply worried about how things will run in my absence, and understandably so. Being how I am, I quickly folded and decided to decline. But then a short while later I got a reassuring phone call, changed my mind and officially accepted the offer. Now tomorrow when I inform the note writer of my decision I will be bringing an extra large tub of butter. With any luck both parties will be at ease with the decision and all will be well.
We all manipulate to some degree day in and day out. Sometimes being completely blunt or completely honest causes more problems than using some subtlety. Some carefully executed manipulation can make sure too many feathers don't get ruffled. People just need to ask themselves beforehand, "Is this truly important?". Sometimes it is.