If it is an old installation and new components are not backwards compatible (e.g. not the same size/shape as older components so don't fit) then you are faced with either re-using an old component or replacing the lot. In that circumstance it may be the client demanding you use a second hand component due to cost implications, but I would suggest the implications should be made clear to the client (probably in writing with his signature to say he has read it).
If it is an old installation and new components are not backwards compatible (e.g. not the same size/shape as older components so don't fit) then you are faced with either re-using an old component or replacing the lot. In that circumstance it may be the client demanding you use a second hand component due to cost implications, but I would suggest the implications should be made clear to the client (probably in writing with his signature to say he has read it).
