AFAIK there are limits to that. Certainly, contracts are required to be reciprocal. That is, one cannot write a contract that states A gives stuff to B, without requiring B to give some form of compensation. This is why things are sometimes sold for $1 rather than gifted.

I think there are also 'no contracts can be made under duress' clauses that limit how much one can use leverage to unbalance a deal. Not sure what kind of limits there are to that though.