How do I know a quality hand knotted Persian rug?

The quality of a hand-knotted carpet can be judged by several factors: the density of knots (the more knots per square metre, the better the quality of the carpet), the material (wool, silk), the symmetry and detail of the pattern, as well as the quality of the dyes used in its production. It is also advisable to look at the back of the carpet where the knots are more visible.