It is somewhat like buying a used car. Look for leaks and the physical condition of things. Does it generally seem cared for, no abnormal noises- that sort of thing. If this is a twin bladed , 20 HP Courage engine - one has to look for oil leaks from the top as engine blocks had cracked on these. The deck should run up smooth, the transaxle should sound quiet, be positive on engagement and not lose power uphills or as it warms. Keep in mind that at Home Depot, you can buy a new 42" Ariens, built by Husqvarna for 999$ with a manual transmission and for a coupla hundred more- basic hydro.