In addition to the more serious issues related to serious distortion or decay as has been discussed, another issue is how the used saddle was broken in by the previous owner’s anatomy. If the previous owner had sit bone configuration close to yours, you will likely make out well with the saddle as with use you will make small adjustments during your own secondary break in. On the other hand, if you are just not a good match to the previous owner, you will not be able to break it in to suit and the saddle is simply damaged beyond repair for your use. Looking at well broken in saddles has opened my eyes to how asymmetrical many pelvises must be….and not everybody sits straight on the saddle as well, which can have the same effect.