Ask private sellers if you would be allowed to take the instrument to a local repair shop for evaluation before buying. Some saxophones are silver plated. A good saxophone will be dent free and clean. Saxophone pads are made of leather and orange in color. Like the flute and clarinet, these pads can be replaced but are more expensive since they are made from leather.
Saxophones have many guards that protect the keys from damage.
Screws that come loose often and fall off hold on all of these guards. This is another item to look for when checking out a used sax. Use common sense when inspecting instruments and if you have any doubts, take the instrument to someone knowledgeable or look for something better. Protection One factor that is usually forgotten is the case or 'gig' bag that protects the instrument while it is unused or being transported from home to school. Hard wood or plastic cases are preferred.