Do not treat all labels as equivalent
A speed limiter, conventional cruise control and adaptive cruise control are different functions. Lane assistance is another question again. Ask the seller to explain the exact feature being advertised instead of relying on a broad phrase such as driving assistant.
Find the relevant controls
With the car parked, locate the controls and settings and read the instructions for that particular vehicle. Record the wording used on the display. Buttons and menu items help frame the question, but they do not prove that the system is fully operational.
Respect operating conditions
Driver assistance functions have limitations and operating conditions. Do not ask for an emergency-braking demonstration. Do not ask anyone to follow another vehicle too closely. The driver must remain attentive to the road. Any driving demonstration must follow the vehicle instructions and safe driving practice.
Separate equipment from confidence
Note whether the function was only described, shown in a menu or demonstrated appropriately. Record warnings and unresolved questions. If a feature is central to your decision, arrange professional inspection rather than inferring its condition from a short drive. The presence of assistance equipment does not turn a car into a self-driving vehicle or remove the driver's responsibility.