First things first... Checking the condition of the camera. For the first listing:
You want to know from the seller how many times the shutter has been fired. I don't see that mentioned anywhere in the listing. The K-5 has an estimated shutter life of 100,000 actuations. There's no reason to shy away from buying a camera with, say, 50,000 actuations - but you would expect it to be priced considerably lower than one with just 10,000.
Looking at the base of the camera, it is quite badly scratched. I'd guess that the camera has been quite heavily used, by someone who isn't all that careful with their equipment. My own K-5 has just one tiny mark near the shutter button, and has a few little scratches, scrapes and little dings on the mount from fitting adapted lenses (which is mainly what I use my K-5 for, now). I've taken a *lot* of shots with that camera, but it still looks very little different to new, because I take very good care of my equipment. A camera with lots of scratches and dings suggests a lack of care from the owner. Not always, but it's a consideration.
Ask if the viewfinder is clean. A few little dust spots don't matter, but it should be generally clear. Also ask if the mirror is clean and unscratched. Some people try to clean the mirror with all sorts of unsuitable items... Ideally, it should never be touched.
Ask if the main LCD display has any stuck or dead pixels. It's not the end of the world if it does, but it can be annoying.
Ask if the camera has any problems at all, however minor - anything that is not explained in the listing.
Ask if it comes with battery, charger, strap, CDs, documentation, box etc. The battery and charger are the most important. If it doesn't come with the strap, will it come with strap rings so you can at least fit one of your own? The strap rings are missing from that camera, and whilst 3rd-party replacements are easy enough to get hold of, you'll have to buy some and wait for them to be delivered.
As for the seller...
Always check feedback level, look at recent sales activity and particularly any recent negative feedback to see what the problems were, and if the seller responded reasonably. Make sure that the seller accepts returns, too. And pay for your transaction via PayPal, so you're covered by eBay and PayPal buyer protection