It can be difficult to know the difference between a machine made Persian rug and and authentic handmade rug. There are machine made rugs that look very much like handmade rugs in every way. One way you can tell, machines do not make knots. A machine will put the wool fiber into place and then use latex to back it. That gives the rug a rough feel to it.
High quality natural wool is sometimes used by the machines and sometimes synthetic wool is used by hand weavers. But there is a way you can test for wool to see if it is natural or synthetic. Take a small thread out of the carpet and burn it to see if it burns and smell like hair. If it doesn’t, the wool is synthetic. Not all natural wool fibers are equal either. To test the quality, vacuum the back and front. Rub your hand across the area you vacuumed and roll the loose fiber in your hand. If it is as thick or thicker that the carpet, it is most likely lower quality. You also need to know the quality of the wool and the density of the knots. If the carpet is sheered too low and the density of the knots is low, the design will not look as good.
The thickness of a Persian rug shouldn’t be relied on to tell if a rug is machine made or hand woven, but having said that, a higher quality rug will have been designed to the right height to show it off to its best advantage.
Look at the front and the back. Is the rug as clear from the back as it is from the front? If there is a unclear and fuzzy look to the back of the carpet, it does not necessarily mean that the knots are too tight. If a fiber strays from a knot, a weaver will sometimes burn the loose strands so it will give that clean look. It is when the weaver does not do this that you see the unclear look.
The only fail-proof way to know if the Persian rug you are looking to purchase is machine made or authentic handmade is to ask for a certificate of authentication. Also, ask the shop owner questions. Odds are he/she will not put his/her reputation on the line to be dishonest about the rug.