I've bought from Premierworld before. Nothing to worry about there. He sells real stuff.
Seiko has a factory in Singapore, so there are no tariffs, nor transportation costs for Singaporean dealers. They're still real Seikos, and mine work flawlessly--I'm wearing my orange monster right now. Oddly enough, I have seen fake Seikos in a local liquor store...they were of such poor quality that Helen Keller could call them out.