Buying a used hot hatch can be fraught with all sorts of pitfalls. Many are thrashed and crashed, some have spent more time on a circuit than on the road and there are others that promise much but fail to deliver. That's certainly not the case with Ford's third generation Focus ST. The first ST, the ST170, was lightweight and a lacking in torque. The second generation model fixed the torque but developed a savage thirst. Third time was the charm, with the ST getting a winning blend of pace and efficiency. Here's what to look for when buying one used.