When it comes to collecting model trains, condition trumps everything. It is the one attribute that can never be corrected once damage has been done and where nearly all the value lies. For postwar and prewar trains, C-8 to C-10 is pretty much guaranteed not to operate until you take them apart and perform a full service. This fact does not dimish their value by even a penny.
Modern era (the last 25 years) is a little different. Cosmetics are still highly important but operation carries a higher importance since the cost to repair will surely be higher. Hence the need for the O rating system in addition to cosmetic condition.
