Note the color of the fur and skin. Sheepskin can not be dazzling white. If fur and skin have a nice creamy shade, you are likely not fake. You should be alerted if the product is a bright creamy or even peach. But one option is hard to judge.
Smell fur. If it is suspicious or synthetic smell the distinct aroma of the dye, sheepskin fake. When buying colored fur, this method is unreliable. But if the thing was correctly processed, even after the color remains subtle smell of natural wool.
Pull the skin in different directions in the area of any seam. If this is genuine sheepskin, the seam will be invisible through the fur, as the skin is stretched. Synthetic materials are less dense and if they pull, you will notice the thread.
Synthetic forgery can be distinguished from the original, if you try to separate the fur and skin. If they break, it is usually the material, which is glued to the fur. When bending the sheepskin should not be seen nor glue, nor any materials. To separate the fur from the skin is impossible.
If you have already bought a fur coat, but you are plagued by vague doubts about its authenticity, then find out it may be a result of wear. Natural sheepskin not hot, but at the same time and not cold. In synthetics, the person begins to constantly sweat and feel uncomfortable.
Buy similar products in major stores with a good reputation. Of course, the price can be much higher, but the chances to buy a fake times are reduced. If you have never bought stuff from sheepskin, before you make a purchase, walk around the different shops to compare how the real product.