If you’re thinking of buying a used wood stove proceed with caution. You should first consult with your fire insurance people who will tell you about the technical requirements and installation, from chimney class to floor covering, placement distances and wall protection.
While new installations are best done by professionals (they know fire regulations), simple replacements of an approved stove are another matter — primarily a matter of all-out work.
I am in the process of replacing an existing workshop stove with a used one. It’s an ancient heavy-duty monster with a huge firebox. There is virtually no metal heat erosion and only one firebrick has been noticeably damaged. However, whatever was being boiled on its surface had run over onto the top and sides resulting in disfiguring but very shallow rust staining (resulting in a low asking price).
An hour with a rotating steel brush in an electric drill worked wonders and after a coat of spray paint the stove looks virtually new. I paid $50 delivered, so for all intents and purposes I have an all-but-new stove ready for hookup for $60 and a couple of hours of labour.