Essentially, if a work of art or an antique is of personal or financial importance, it pays to get a second opinion if you don't much care for the first one. The job of an expert is to use acquired skills and natural gifts to narrow the gap between opinion and fact. The better the expert, the more narrow the gap—but it never disappears entirely. Experience teaches collectors, dealers and art historians that mistakes are unavoidable. Learning from them is often more beneficial and less expensive than going to court.
And in a timely coincidence, a piece from the New York Times on avoiding buying fakes. Endearingly, it's from a column titled 'Wealth matters', and includes this sentence in its preamble: "I know enough about the art world to know that is a secretive, clubby place with more than its fair share of eccentrics."