2003 Hyundai Accent Sensor?

Im looking at buying the car off a site from someone and the owner of this make and model writes "the car is running well, but sometimes a sensor or something else from the transmission doesn’t work right so it starts in the second gear. When I shut off the engine and start again than the car drives normal again" what does this mean? And how much is the cost to fix this problem so in the end is this worth buying and fixing?