The lining above your head on the underside of the roof. Headliners are usually not a problem. However, sometimes they are faded or have stains or tears. They can be replaced, but this requires some time and expense. Upholstery Should be clean and not faded or ripped.
Leather is a special case.
It usually has some added value if it is in good shape. However, if it needs repair or replacing it is much more expensive than cloth or vinyl to do so. Carpets Older cars usually have some carpet wear. If so, it must be replaced for the vehicle to be worth top dollar. Any stains will reduce the value.