I have my doubts as well. Best thing to do would be to try to find the identical item in an online store or B&M store, since it is probably unlikely that a counterfeiter has the same pattern. Even then, still possible.
I don't know if Etro is a big enough name to be faking.. you guys know better. But this one does seem odd. Like Norcal, the buttons lack the "etro" engraved name. Also the embroidered Pegasus is poorly done, plus the fabric/pattern of the shirt looks as if it were from the more casual shirt line of Etro, but it lacks the buttondown collar. Their dressier shirts are also wildly coloured, but the fabric is much much better and the collars are not buttoned down. This one looks like a mongrel.