Even if you have a perfect offer and a perfect acceptance, you still need to have proper consideration.

That is an act or a forbearance from an act that is bargained for and received by one party from the other, which motivates you to do something.  In layman's terms, it's something that each side must do, which somehow inconveniences the party.  Though this consideration does not need to be valuable or even equitable, it must not be grossly inadequate to the point that it tends to indicate fraud.