The "guy" may have told you wrong; P0500 vehicle speed sensor malfunction. Are you sure the code is correct? Take it to an auto parts store and have them read the Diagnostic Trouble Code. They will do it for free. Some people have changed the brake switch at the brake peddle to remove the bas/esp light. However that fix normally doesn't throw a code. A good Mercedes independent shop can tell you which speed sensor/wheel is bad. It is a simple fix to change a wheel speed sensor.