Take the basic front seat. There is a fold in the LEATHER. Leatherette(FAKE!!) does not have this fold. Please examine the difference between the two photos. The first one has leather, the second does not.
There's an even easier way to tell. If it's cracked, faded, stained, creased and generally just looks like crap, it's leather. Leatherette, being a synthetic material, will have an uncanny "factory perfect" appearance and feel even in an older car. It does not age or wear quickly from exposure to water or UV radiation. Leatherette will not stain, wrinkle, or fade. And the smell is different too..