Back in 2009 I started looking for a California.
Have searched a lot, but did not manage to go looking in person to one.
It were all first generation T5's with the 5 cylinder TDI, all about 5 years old and all more than 100 000 km.
All prices were between € 40 000 and € 45 000. I have then visited my VW dealer, and found out that I could buy a brand new one for less than € 50 000. Took me a couple of days to overthink that and finally went for the brand new one.
As I am very carefull with my own properties, and had seen a couple of California's, the choice was not that hard in the end.
My California is cleaner after a 2 weeks holiday, living in it 24/7 (if not out on a bike trip or walking trip), and now even after over 9 years than most normal cars that are only used for commuting.
The choice is all up to you, but when you buy a second hand you never know what has all happened with the van, or what is coming your way sooner or later.
If you buy a new one, one could only hope that it came out of the factory, straight to the dealer without having to pass to a bodyshop, or a workshop for repairing transportation damage. But in most cases, a new one is immaculate.
In the end, it is your own decision. If you can find a decent T5.1 (180 hp??), there must be no problem, but you never know when it really is a decent one. The owner may look trustworthy, and the van too, but they might just be keeping up appearances.