Let me offer you a warm welcome to the forum.
The short version of my answer to your question is: if everything is in good order, it's a great deal. Check the number of shutter-actuations though - if it's over 25.000 it's rather used. Still, some good lenses there.
The K100D's 6 MP is plenty and you can easily do 18X12 inch prints with that.
With the body's built-in shake-reduction (which was considered very good for it's day back n the latter half of 2006 when it was introduced) and the lens-mount that allows you to use pretty much any lens Pentax has ever made, it's a versatile package.
The built-in flash and the kit-lens (18-55) are both really good for the class and it's ability to use AA batteries makes it very versatile.
The auto focus is a little on the slow side - more so indoors in low light. The auto-white balance can struggle with incandescent lights, but you will learn to adjust for that.
From a value-for-money perspective (assuming everything is in good order) I think it's a good deal.
From a so-how-much-has-other-entry-level-DSLRs-evolved-since-then-and-what-do-they-cost-now perspective (lol) I still think it's a good deal. Things haven't changed that dramatically - a slight improvement in the high-ISO noise-handling perhaps, but nothing to gasp excitedly about - ISO800 and up has perhaps gotten a little better. A few more in-camera features - most of which you can get better by post-processing on your computer.
I would strongly suggest that you try to handle the camera first. Many people find that the control-scheme, weight and overall "feel" of a camera means a lot more than they imagined. This can have a significant impact on the "shooting pleasure" in both directions.
Good luck with your choice, whatever it may be.