The relevant metric for deciding if something is rare (in this context) is the number of available substitutes, including by other artists, not uniqueness. A sn

The relevant metric for deciding if something is rare (in this context) is the number of available substitutes, including by other artists, not uniqueness. A snowflake is unique, but not rare. The artist concerned here "is considered as one of New Zealand's leading artists" and has a "unique painting style", and so there are very few paintings that are like his, and (probably crucially, although I'm not familiar with the specifics) plays a role in New Zealand national identity. You can get plenty of expressive landscape paintings, in the sort of style of an unimaginative Van Gogh, produced by hundreds of artists throughout the 20th century, and most are perfectly pleasurable to look at, but you've never heard of the artists, and the works are easily available for hundreds to a few thousand dollars -- because they are not rare, it doesn't particular matter which of the many available paintings you end up buying, as long as you enjoy looking at it.