Are you saying that they corrected the AF in addition to correcting the back focus (whatever that is) that they say they did?

Yes, on the 'before' image the street sign has an odd halo around it in addition to being blurred.

In both cases, everything was set to auto and resulted in:-

Before - f5.6, 1/100 sec, iso 100, 50mm

After - f8, 1/80 sec, iso 200, 50mm

Hmm. I'm new to this forum, so maybe I've not done this correctly.

The images I sent were each about 7mb. The ones on the forum are 500k. With that reduction in size and resolution, I don't think you will be able to see the differences I was referring to.

Zoom by 100% and look at the road sign in the centre of the picture. The before picture was taken on a day with light cloud, the after one was taken on a dark cloudy day, with a slight mist, which to me makes the improvement all the more remarkable.

Having previously owned a Pentax Spotmatic and a Pentax P30 I recently bought a Pentax K-50 with a SMC Pentax-DAL 18-55mm AL WR lens. After my initial delight in handling a Pentax again, I was disappointed to find that the sharpness of the images was no better than my ten year old compact camera. Initially I thought that the less than positive reviews I have read about kit lenses must indeed be true, but after a while I just couldn't believe that with so much more glass the image could be relatively poor.

I returned the camera to Pentax service who adjusted the back focus. The images taken with the 18-55mm lens are now better than the compact camera, and appear to be the equal of images taken with the SMC Pentax-A 50mm prime lens from my P30.

I have read elsewhere about quality control problems with current day Pentax cameras, so if you suspect something is wrong with your new Pentax, my advice is to get straight back to them and ask for it to be fixed.