Thanks for the positive comments about my S&W 3rd Gens.
I think one has to keep in mind that not all 3rds are the same. In the first photo, that 645 (I bought in late 2009) was the first I had run across in as-new-in-the-box condition while hunting for S&W autos. The pistol is basically perfect. So, I paid the asking $650 price.
In the "big boys" photo, the three on the right are 10mm pistols. They were only made for a year or two. Thus, the production figures are limited. Now, the 4576 (bottom, left) was around 97% condition without a box. I found it on consignment in early 2007. It was around $600. I thought that was a little high, but I had never seen or even heard of one. I bought it. According to the factory letter I obtained on it, only 1,386 of these were made. They are hard to come by.
In the fourth photo, (single-stack compacts), the blue pistol is a 4014. I found it listed at a store quite a distance from my home. The price was around $400 in 99%, no box. Again, I had never seen one of these and figured not many had been made. I was correct; the factory letter states there were only 550 made. Because it has a black alloy frame, it's very hard to find in 99% condition.
My point here is that there is big difference between these 3rd gens and the ubiquitous 5906, 4006, 4506 or 6906. The latter were used by many, many LE agencies around the U.S. They are found almost everywhere in condition ranging from trashed to NIB. They are not hard to find. While I do have one of each of those, I do not seek them out nor do I pay much for them.
The 3913 is a market unto itself. There were a whole lot of these made and should be relatively cheap. However, they're also sought out by whole lot of guys. In other words, they have a very, very strong following. I have three myself, an early one (1992), a late one with night sights (1996), and a TSW pre-rail (1999). Note the pre-rail was only offered for two years and is harder to find then the ones with the rail.
Here's an example of what I'm talking about. The 6904 (fifth photo) is the blue version of the 6906. The blue 3rd gens were not nearly as popular as the silvers pistols. There are far fewer blues around; next time you're at a gun show keep count of how many blues you see. In addition, the blues, with their black alloy frames, show every nick and scratch. So, finding one in 99%+ condition becomes problematic. Assuming both pistols are 99% condition, I would pay more (probably 20% or so) for the blue.
Another example, I sold my 99% 5906, but kept my 99% 5903 and 99% 915. Why did I keep the ones I did? During my years of looking, the 5903 (alloy frame 5906) that I bought without box was the only one I'd seen in that condition. The 915 I purchased was the only one of those in that condition I'd seen. On the other hand, I'd seen many, many 5906 pistols ranging from 95% to NIB.
Final example, I had two 4006 pistols, both in 99% condition. The one I kept was the only one I'd seen with factory adjustable sights. The one I sold was one of many, many I'd seen over the years.
IMHO, as these pistols become more collectable, these are the things that will make a difference in pricing.
FWIW