You weren't tricked. If you have the EVIC (electronic vehicle information center) it will show the pressure from all four tires. You know if you have the evic if the screen under the speedometer has a small knob on it and it lights up with info. If you don't have that system it will only notify you if your tires drop below a preset pressure,about 26psi if I'm not mistaken. The car will not tell you which tire is low it will indicate it with a symbol like this, (!) that is displayed above the odometer.