Some timber species that are not marketed any more due to scarcity, are only available second-hand. Bringing out the best in timbers that have previously been painted or stained, takes patience and a degree of skill. Dipping in caustic soda can leave timber with a faded and 'furry' surface if it is soaked too long. Sanding along the grain works well on straight sections, so long as the timber has not been undercoated with a paint that clogs up the sandpaper. Paint on carved or turned wood may be removed with any of a variety of metal scraping devices or by scratching with a fragment of glass.
Paint remover can be a help for otherwise inaccessible places, but use it sparingly.
Nails should always be removed, not sawn off. Oxalic acid can be applied to remove metallic surface stains. Secondhand stud framing is usually dry, making it ideal for joinery work. However, second-hand materials need to be selected by the user. A builder can reasonably be expected to put in recycled materials, but not to seek them out.