There is no way to ensure that a used wheelchair will fit a new user's needs. The new user's weight, width, terrain (for indoor/outdoor use), physical limitations and capabilities, etc., will all affect the durability of a used wheelchair.
Wheelchairs are highly specialized products that require the collective input of a doctor, therapist, mobility equipment provider and potential user to ensure that an appropriate piece of equipment is matched to the user. Since wheelchairs are individually tailored medical devices they are generally not meant for resale.
However, it is understandable with the mounting costs of health care and the cuts to government funding, that mobility users might need to seek cheaper alternatives, like used wheelchairs or scooters. If you decide to purchase a used wheelchair, please ensure that your weight and size is within the specified weight/size capacities of the used wheelchair.
'Used Wheelchair For Sale' ads on the bulletin boards, websites and newsletters at your local rehabilitation hospital, independent living center, State Rehabilitation Department or local disability organization can be valuable resources for used mobility equipment because the staff at these organizations have your best interests in mind. Ads that appear in the classified pages of newspapers, on eBay or used wheelchairs that appear in pawn shops are not valuable resources as there is no professional standard governing these sales.
It is important to remember that second-hand used wheelchairs don't have transferable warranties. This means that even if the warranty was still valid under the previous owner, it won't be valid if the wheelchair switches owners. This is the FDA's way making sure mobility equipment is being used by the proper individuals.