Some do, others don't.
As an example, a large bottle of Singha off the supermarket shelf is 47 - 48 baht. The shop at the entrance to my main soi charges 50 baht out of the fridge. Once when the beers were in for less than an hour, he told me, they're not really cold, as in would I still want them for that price?
The shop further in the soi charges 55 baht, but his beers are always cold. For obvious reasons I tend to avoid this shop.
SJ, you won't notice it if you're not looking for it. But I have also been known to have paid more for a
small bottle of chilled said brew through the persuasive nature of a pretty girl in a short skirt that happened to be sitting on my lap at that particular moment...
