First, an expert provides a description of a work of art, which involves issues of authentification and even attribution. Once these have been settled, an expert will then provide an appraisal. The first process requires knowledge of art history, while the second involves a good understanding of the art market. This is why experts must be extremely familiar with how the market operates, with the ability to decipher results available online. In the art world, taking readily available information at face value – even when it is not free of charge – is the best way to under- or over-estimate the value of an artwork. This leads to disappointment when the work sells – or when it doesn't sell at all.
That being said, although experts are better placed than their clients when it comes to appraising a work of art, prudence should be their watchword. A jack-of-all-trades is generally a master of none. How could anyone hope to develop an expertise in such widely differing fields as old master paintings, silver, carpets and period furniture? This is, at any rate, our view of expertise.