They had been left at the roadside about 15km away, near Hawke's Bay Airport, when a prospective buyer leapt into the car and drove off.
It was seen in traffic near central Napier soon afterwards and crashed a few minutes later after racing out of the urban area while being chased by police.
Sergeant Ray Wylie said the driver refused to stop and the car went up a bank, hit a fence and flipped, coming to rest upside down.
The woman was was uninjured and was arrested at the scene.
A spokesman for Hawke's Bay Toyota said a woman entered the Napier branch earlier in the afternoon inquiring about a vehicle on the sales lot.
As she did not have an appropriate licence, she was not allowed to drive the car but accompanied a staff member on a test drive, he said.
It was while they were parked at the side of State Highway 2 and inspecting the vehicle from the outside that the woman got back into the car and drove away.