Fake pre's usually have spelling mistakes on their box or on pre.
Fake pre has cheap build quality, cheap plastics. Original ones have good finish.
Fake ones usually dont produce good sound when mated with original speakers.
Fake ones have software errors.
And the last but not least the fake ones are less priced and shopkeepers tell that it is original or if anyone asks why selling for low price then they say this is smuggled product.
Market nowadays is full of fake products. You can find 3 prices for single speaker. I am not saying that if one sells at highest price the product is original, but mostly the expensive ones are originals. And sometimes fakes ones are also sold at original price so that customer doesn't get any doubt in his mind. By little bargain they sell it out. And buy your products froma reliable source a shopkeeper who keeps all original products or you usually buy from him.