Cost - typically, artificial silk items will cost less. If the item is cheaply priced, then as a general rule the chances are that it is not genuine silk.
Colour - silk usually reflects some light and will be coated, meaning the colour will not look ‘flat’ and will shimmer. If the colouring of the silk looks like a flat, block colour, then chances are it is not real silk.
Smell - if you want to test whether silk is real, take a few strands of the material and set it on fire. When burning, it will smell like burnt hair - which is a very strong, unmistakable smell.
Invisible flame - when burnt, silk will also burn with an invisible flame, and the burning will stop as soon as the flame source is removed.
Touch - if you rub a piece of silk between your fingers for a while then the material will become warm. If it stays the same temperature, then it is not genuine silk.
It’s labelled as satin - satin does not mean silk. Some may get the two confused, but satin products are often far cheaper than silk products.
The ring test - pulling silk through a ring is a traditional way of checking its authenticity. The ring will slide smoothly over real silk, while fake silk will often bunch or get caught on the ring.