Cheapest I've found in Malaysia is in Langkawi. Even when compared to other duty free islands like Tioman and Labuan.

Buy from more reputable chains to reduce likelyhood of landing with a counterfeit. Poor reputation comes back to bite the shops, and bigger chains can't afford that. So far, bottles that I bring across on my monthly trips are safe. Yamazaki, Glen-xxx, Mckellan, wines....

Hardly any stories of low grade or counterfeit beer these days. Margins too small.