The K-7 is a great camera. The production has been discontinued and the K-5 is taking over as the semi-pro Pentax dSLR. All these contribute to the lower 2nd marketplace prices and the K-7 is a very attractive offer now for many.
Make no mistake that the K-7 is still one of the best dSLRs on the market for its ergonomics, its viewfinder, its handling and solidity. All these features were re-used without any improvement on the K-5, and that does say a lot...
The weakness of the K-7 is its low-light conditions where the K-x (and now K-r & K-5) excels. However there are some well-known techniques to improve drastically the performances of the K-7 in low light:
* shoot with zero (no) in-camera processing and PP your shots with dedicated noise reduction softwares; I use Noiseware, others use Noise Ninja and co; importantly this works very well;
* use Adam's solution with in-camera High-ISONoise Reduction: {https://www.pentaxforums.com/forums/pentax-dslr-discussion/106600-k-7-high-iso-success.html};
* use a fast prime lens (large aperture, low f like f1.4)
There have been several threads on the topic:
https://www.pentaxforums.com/forums/pentax-dslr-discussion/121531-k7-high-iso-noise.html https://www.pentaxforums.com/forums/pentax-dslr-discussion/118450-post-your-k...iso-shots.html https://www.pentaxforums.com/forums/pentax-dslr-discussion/118044-k-7-opinion...-shooting.html
All in all the K-7 is a great camera, As time passes by, it has been superseeded and the marketplace prices reflect the situation. It is however one rare Pentax dSLR that did not have some fundamental flaw like others (battery drain in K-x, sensor stain of K-5).
A key feature of the Pentax line-up is also the compatibility of lenses. Indeed the lenses are more important than the camera body: "a lens is worth every penny".
Food for thought from a very happy K-7 owner.