How can we identify if a lacoste shirts are 100% authentic or fake?

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Here in the philippines, we rather buy an affordable shirts than the expensive one, but there are some shirts that almost near to the perfection that it almost mimic the authentic quality of lacoste., and it would just cost 10$., but still, there are difference betweeen the two, until now, i can't still identify what is the authentic, anyone knows how to identify an original lacoste? thanx!