Final answer:
A customer can sue Whitmore on the basis of vicarious liability because the principal is liable for torts committed by an agent within the scope of their agency.
Step-by-step explanation:
If a customer is injured in an accident caused solely by Chamber's careless driving, that customer can sue Whitmore because the principal is liable for torts of an agent acting within the scope of the agency. This principle is rooted in the concept of vicarious liability, where a principal is held responsible for the actions of their agents that occur during the course of their employment. By being on duty and engaging in activities related to sales representation (which could include driving a vehicle), Chambers's actions would likely be considered within the scope of their agency relationship with Whitmore.