How can you distinguish between a real leather from a phony leather?

Its soft, very soft. And its light, its unbelievably light(really unbelievably). I don't know about the smell and all. But even if you slightly bend it, it gets wrinkles. Not hideous looking wrinkles, but wrinkles that tell you how soft it really is... Even if you feel its a bit rough, then its not leather at all...

Since I don't buy leather, I have to know how to distinguish it. You can often tell by the smell. But sometimes that isn't possible. Usually there is a tag somewhere on the product that says what it is made of. If it says "all man made materials" then that is not leather. If it says "leather" "PU" or something like that, that's real leather. I don't usually trust the sales staff because they won't likely know unless it says on the tag or something, in which case you can read it yourself.