The following information will help you to better understand the many factors involved in establishing value.
This section covers the terminology regarding the different condition levels. Understanding the meaning of each class is very important. Listed below are the standard 5 levels of condition and their definitions:  See Price Guides for current vehicle valuations.

Vehicle Condition Scale
  1. EXCELLENT or CLASS 1 Condition: Professional frame off restoration of all areas of the vehicle, restored to an "as new condition". An original vehicle with all components in "as new" condition.

  2. FINE or CLASS 2 Condition: Well-restored or a combination of superior restoration and excellent original components; or an extremely well maintained original vehicle showing very minimal wear.

  3. VERY GOOD or CLASS 3 Condition: A completely operable original; or an older restoration showing wear; or amateur restoration.  Also a combination of a well-done restoration and good condition original; or a complete, partly restored original with NOS parts. All areas presentable and serviceable inside and out.

  4. GOOD or CLASS 4 Condition: A derivable vehicle needing little or no repair to be functional; or a deteriorated restoration; or a poor amateur restoration.

  5. RESTORABLE or CLASS 5 Condition:   Needs complete restoration of all areas; not derivable, but is not weathered, wrecked or stripped to the degree of a parts vehicle.
As you read through the different conditions, little red flags start popping up everywhere.  One of the first questions many people ask is "I didn't see any class for Show Trucks". What's a show truck?  I have seen just about every Class truck represented as a "Show Truck" at one time or another.  If your talking about a real touring show truck, then expect to pay what the owner has invested. These trucks go for whatever the involved parties agree to.
Keep in mind, restoration labor costs should not be represented in any selling price. An example would be if you were to spend 400 hours restoring a Ford Pinto. When you were finished, you might have a fine looking Pinto, but it wouldn't be worth any more than it's market value for it's condition.
Next, you see in the Class 1 section the words "Professional Restoration". It refers to the type of work, not who did the work. Amateur restorer's can do "Professional" quality work. And, in turn, professional restorer's can and do amateur looking work at times. So, you need to look very close at any type of restoration work claimed.
You'll also notice there's not a class that refers to parts or stripped vehicles. Because the level of completeness can vary greatly, no value can be set. Don't let anyone tell you a parts vehicle has a "Book Value". There is no book value for parts or incomplete vehicles.
The best way I have found to fairly arrive at a value for a incomplete vehicle, is to subtract the replacement cost of the incomplete parts from the Class 5 value. Sometimes,  you might find that the seller would owe you money. When this happens, you have to ask yourself if you really want to restore the vehicle. If you only want the vehicle for parts, then your in a pure negotiation situation. - CTS