Plea bargaining in the United States
The constitutionality of plea bargaining was established by "Brady v. United States" in 1970, although the Supreme Court warned that plea incentives which were sufficiently large or coercive as to over-rule defendants' abilities to act freely, or used in a manner giving rise to a significant number of innocent people pleading guilty, might be prohibited or lead to concerns over constitutionality. "Santobello v. New York" added that when plea bargains are broken, legal remedies exist.
Illusory promise
Many judges would consider the "bargaining for a percentage of the proceeds" example above an enforceable contract, even without an implied-in-fact or implied-in-law good faith term. They would view the opportunity to enter into a business relationship to itself be acceptable consideration. Put differently, the mere possibility that the promisor would do business is a valuable product of the bargain even if he does not do anything. Of course, if the promisor entered into the relationship purely with the intent of fraudulently harming the promisee, he could be cited for fraud or bad faith principles that apply to all contracts.