Quite simply they are bootlegs and the quality will vary between set. Its really hit and miss with what you get, some will be great whilst others will be the biggest waste of money.
Adrico, be careful -- U.S., European, and Asian DVDs often are in different formats. Check out whether you'll actually be able to play that Japanese DVD set on your machine.
Yeah Darth, I mean Welsh, it looks great. I have seen the picture of your colection before but I had never noticed the Columbo picture when they are all together.
They are very expensive. I think it works out something like £60 per box of 2 volumes. Each volume only has 2 episodes. I was lucky enough to find the complete collection on ebay and bought that.
There is someone selling the complete set now. Heres the link