Influence

Internal Consistency

Desire to be consistent with a promise made or a prior position taken.

Expectations

Setting a positive expectation 

Involvement

Involve people or solicit their ideas

Scarcity

Make it more attractive by making it more scarce

Contrast

More attractive by comparing with something else (Used to be $30, now $20)

Esteem

Praise and recognition

Obligation

A favor creates a sense of obligation