NADA values for used Fifth Wheels

I'm in the market for a Fifth Wheel and from what I'm seeing so far either people are mighty proud of their Fifth Wheels or they seem to hold their value really well. Most that I look at are priced above NADA value. I've inquired on a few and when I tell them they are priced above value they say then move along. That's what I'm asking for it and don't make me these silly offers. So I've always been taught that when you book a vehicle the only extras you can add on when getting a used value are extras. People are adding in there A/C units, furnaces, refrigerators, slides, awnings, gel coat exteriors etc when they are already included in the book price. So basically they are adding them in twice making their values sometimes up to $10k higher than it should be. It even says in the fine print when you book out an RV that you do not include any items that come standard on the RV when purchase. The things I mentioned above are standard items.

Am I wrong for pointing this out to sellers? And why are people paying over book value for these units? Just curious. What are your thoughts on used RV values.