Pierre Valentin of Withers answers some questions from the FT for their Ask the Expert column:

This is where the art adviser comes in. Naive buyers often rely solely on the advice of the dealer or auction house. They do not realise that the dealer or auction house generally acts for the seller, or even for themselves if the dealer sells from stock. This results in the interests of the buyer and those of the dealer or auction house being diametrically opposed.

Unfortunately there is a significant risk that collectors will buy a fake. While it is impossible to stop this from happening, the likelihood can be minimised. Even if you buy from a living artist, you cannot be sure you are getting the real deal. Artists such as Giorgio de Chirico, the Italian Surrealist painter, were known for disowning their own work if they no longer liked it. There is a story of Pablo Picasso authenticating a fake by signing it, because he felt sorry for the dealer who had sold it as an original.

Ask the Expert: Be Smart About Art (Financial Times)