This is what ive found.
Hi, I would advise you to not buy any A&F from thailand. Every item I have brought from there is clearly fake. A&F is actually made in asia but this is not in thailand I would still not advise you to buy from sellers in thailand.
On shirts I have found you can tell whether they are authentic or not by little details such as on the casual shirts there SHOULD BE 'Abercrombie & Fitch' imprinted on every button and on the neck underneath the collar there should be 'Abercrombie and fitch' embroided across the neck. Many fakes dont have these features and have plain pearl buttons or no embroidery on the back of the neck.
Hope this helps with buying casual shirts.