The objective evidence to support the defendants' contention that they were just kidding when they agreed to sell the farm would depend on the specific circumstances of the case. This could include the tone of the conversation, the context in which the agreement was made, any prior history of similar jokes between the parties, and the reactions of any witnesses present at the time of the agreement.

Even if the defendants truly believed that the agreement was a joke, it may not make a difference in the eyes of the law. The legal system often uses an objective standard to determine the seriousness of intention, meaning it focuses on how a reasonable person would interpret the situation, rather than the subjective beliefs of the individuals involved.

The law uses an objective standard to determine the seriousness of intention as a matter of public policy because it provides a more consistent and predictable standard. A subjective standard would require delving into the personal thoughts and feelings of the parties involved, which can be difficult to prove and may vary greatly from person to person. An objective standard allows for a more uniform application of the law.

In the scenario with Mary and Jason, it could be argued that the parties have a contract. Mary made an offer to sell her car for $$50,$ and Jason accepted the offer. However, it could also be argued that Mary's statement was made in frustration and was not a serious offer. The determination would likely depend on the specific facts of the situation, including Mary's tone and demeanor at the time of the statement, and whether Jason reasonably believed that Mary was serious about selling her car.