Thousands of items are available to buy from dealers online. Here we pick out one that caught our eye this week.
Harrison & van Oostende Fine Art, a pair of London dealers, have launched their careers by sourcing misattributed works by major artists, such as this lost autograph portrait by Peter Lely (1618-80).
Offered for a price in the region of £45,000, it shows George Villiers, 4th Viscount Grandison, the uncle of Barbara Villiers. She was mistress to Charles II. Painted c.1668, the oil on canvas measures 2ft 6in x 2ft 1in (76 x 64cm) and has been part of various private collections.