Everyone has their problems, and it's up to them how they react. Most people have guidelines, or social folkways and moraes to instruct them on how to act. People have patterns to how they react to heartache, depression, sorrow, etc.
People also have these same patterns for joy and happiness. Each person has a set way of reaction they have learned through the years. It is possible to predict these patterns accordingly. This can cause people to be manupulative.
Based on the fact that these set patterns to joy and sadness can be predicted from person to person, one can choose whether or not to be manipulative. So does this mean people actually choose whether or not they are manipulated? Just by the way they might react to joy/sadness? Possibly yes. Possibly no.
All and all, it's never anyone's fault. After all, we are only human.