Final answer:
The best response to a customer undecided after a test drive is to respect their need for further consideration and provide them with a business card for future questions, thereby building trust for a potential future sale.
Step-by-step explanation:
The optimal response to a customer who after a test drive decides to continue looking at other options would be option c: 'I agree. You should give your decision more thought. It is important that you are 100% satisfied. Here is my business card in case you have additional questions.' This option respects the customer's need for further consideration, while professionally offering assistance for future inquiries, and ensures they have a way to reach out with a business card. Demonstrating understanding and patience along with a willingness to be contacted for further questions can help build trust and potentially lead to a future sale.