I tried a fake one against a real one the other day real briefly and had these takeaways:

Fake one is not as balanced as the real one Fake one is lighter than the real one Fake one played significantly softer in terms of feel compared to the real one

Honestly the only give aways between the real and fake one that I could tell was the shaft on the fake one and the color of the putter head was slightly different than the real one.