Final answer:
Sarah's agency agreement with the puppy mill ends when the purpose is fulfilled, if terminated by either party, or due to illegal or changed circumstances affecting the agency.
Step-by-step explanation:
The agency agreement between Sarah and the puppy mill typically ends under specific circumstances. This can occur through mutual agreement upon the completion of the purpose of the agency, namely selling the puppies. Additionally, the agreement could be terminated for cause if Sarah's actions were illegal or against public policy, such as knowingly selling puppies from a puppy mill without disclosures. Furthermore, an agency can end due to expiration, where an agency relationship with a specified duration concludes automatically after the agreed period lapses. Another possibility is revocation or renunciation where either the principal (puppy mill) or the agent (Sarah) decides to end the relationship. The agency could also be terminated due to changed circumstances, such as new laws affecting puppy mills, which might make the sales and shipping arrangements Sarah was engaged in illegal, altering the ability of either party to perform under the agreement.