The most important thing to remember when test driving a used car is you are the customer. That's how you test drive a used car. The customer is always right. You set the agenda when it comes to your test drive not the sales rep or the owner if its a private sale. If any aspect of the test drive makes you feel uncomfortable walk away. Trust your gut feelings.
Preparation is key. Make sure youre an informed used-car shopper before taking the test drive. A little homework will put you in a used car that exceeds your expectations.
Also, this isnt the time to diagnose problems. Thats not your goal in a test drive. You want to identify problems for your mechanic to inspect and offer solutions, including price. Dont try to solve a cars problems during the test drive.