Put it in the dark with no water for the next couple of months. If it's still looking green and "healthy" then its fake. Otherwise push the point of a needle into the stem and if juices seep out then you know it's a living plant. If you can't insert the needle then it's fake.
If you can't tell, what difference does it make? I use fake flowers outside in places they won't grow. Looks good to me. Don't give a damn what anyone else thinks. I live my life not theirs and vice versa.
Two days ago bought a pot of cactus, colleagues say looks fake.
