
I call this a tailor's shop, but the business is really much broader than this. They will, of course, alter and custom fit clothing. But what you really go to a place like this for is to pick out fabric—and have custom suits and to other finery made up for you.
If you go to Thailand, and you need nice business clothes, take some time out and go to a place like this.
I will spare you my Veblen-esque commentary on why we feel we need fancy clothes.