Hello,
I'm not entirely sure, but I believe the Kawai X02 may be a piano that was originally manufactured and used in Japan. The Japanese usually don't keep pianos for very long, ie. 5 years or so, before they buy another new piano. Not very many Japanese want to buy a used piano, so a lot of them are sold to piano dealers in North America. This is what I think the history is of the Kawai X02 that you're interested in.
When I was in the market for a piano in Canada, the piano dealer had a Kawai X02 or Kawai X05 in his store. He said that it was originally used in Japan and that they had bought quite a few of these used pianos to be sold in their store. I ended up buying a used Kawai KU-30 piano. It was also advertised as 50" tall by this piano store, but when I measured it at home, it was about 49 inches tall. Even though it was a used piano from Japan, I liked the sound of this piano and it was about six years old at the time. Before I bought it, I paid to have an independent registered piano technician thoroughly exam the piano. He said the KU-30 was in excellent condition and that it should be more than adequate throughout all the upper piano grades of the Royal Conservatory of Music.
I have had the piano for two years now and I have not had any problems with this piano which has made and used in Japan, contrary to all the controversy about grey market Japanese pianos being sold in North America and the extreme temperature and humidity differences between North America and Japan. My piano still sounds nice and there has been no warping of any of the wood on the piano.
If the X02 is US$4,000, then it sounds a little bit high if it was originally used in Japan and then shipped to North America. Perhaps you could ask the owner more questions about this model and bargain a little more.
Remember to play all the notes to see how they sound and have a qualified piano technician inspect the piano before you buy. The cost of this service will be well worth it, especially, if he/she finds something wrong. Do not use the piano dealer's piano technician. You want an unbiased opinion, so research and bring your own technician.