Which of the following must all scales used in commercial transactions display?

In commercial transactions, it is essential for scales to provide accurate measurements to ensure fairness in trade. The presence of the official Weights and Measures seal and registration certificate indicates that a scale has been tested and certified for accuracy and reliability by the appropriate regulatory body. This certification is crucial as it assures consumers and businesses alike that they are getting a fair deal based on precise measurements.

While other factors such as the manufacturer's warranty, product pricing, and expiration dates may be relevant in specific contexts, they do not directly pertain to the fundamental requirement for scales in commercial use to guarantee accuracy and compliance with regulations. Thus, the official Weights and Measures seal and registration certification serves as a vital assurance of the scale's reliability, making it the correct answer.