How do I spot a forgery and verify that a work is genuine?

Authenticity does not rest on a single piece of paper but on several pillars: an expert's opinion, an entry in the catalogue raisonné (the list of an artist's entire documented output), documented provenance and technical analysis. Blockchain is now helping too, as an unalterable certificate of origin, along with artificial intelligence trained to recognise an artist's hand. Be on your guard whenever the price is suspiciously low, the origin hazy and the documentation missing — that is where the risk of a forgery most often lies.