Which of the following is NOT a characteristic of an efficient market solution to externalities?

An efficient market solution to externalities is characterized by the ability of parties to negotiate outcomes that lead to optimal resource allocation, effectively internalizing the external costs or benefits associated with their actions. High transaction costs, however, are a significant barrier to this process. When transaction costs are high, parties may be unable to engage in negotiations or may find it prohibitively expensive to reach agreements. This impedes the potential for achieving efficient outcomes, as it prevents the parties affected by the externality from effectively bargaining and coming to a mutually beneficial solution.

In contrast, the other characteristics listed—willingness to negotiate, clear property rights, and effective bargaining—are all essential components of achieving efficiency in the market. Willingness to negotiate indicates that parties are open to discussions, and clear property rights help in delineating who is responsible for the externalities. Effective bargaining supports the idea that parties can reach agreements that reflect the true value of the costs or benefits involved. Therefore, high transaction costs are distinctly not a characteristic of efficient market solutions to externalities, making it the correct answer.