Singapore is a great place to buy used watches. There are plenty of official Rolex, Patek Phillippe and Omega showrooms as-well-as shops selling second hand watches in Singapore.

I spent a week in Singapore, walking endless kilometers in various malls – old and new – to find the best places to buy watches in Singapore.
1. Far East Plaza
You will find two second hand watch shops at the second floor of Far East Plaza. I also found them to be selling brand new, unworn Rolex Submariner no-date for S$12500, so yes, if you are lucky, you will find some unworn, fully stickered Rolex watches. There were few Audemars Piguet and Omega watches too, but you will soon realize how Rolex focused those watches are.
Omega watches are easier to find in Singapore since they have dedicated boutiques and showrooms in myriad malls. But, if are you looking for Rolex models, including ladies watches, you will have to stick to Far East Plaza. Keep in mind they also have few models of Patek Philippe but all cost more than S$100,000, which is not unusual for a Nautilus. Also, if you want to get your watch fixed, there are shops for that as well. This is a fairly old mall that has turned into aftermarket luxury watch and ladies bag showrooms.
2. Lucky Plaza
There are few watches at the entrance of Lucky Plaza that is just 350 meter away from Far East Plaza. Just get out of the Far East and ask anyone for directions to Lucky Plaza. Within 5 minutes of walk, you will be inside and you will be greeted with 2-3 luxury watch shops. Prices of some of the watches being sold here were slightly higher than the ones in Far East Plaza. Either way, I suggest roaming in both Far East and Lucky Plaza before spending your money on a Rolex or any other luxury watch like Omega or Audemars Piguet.
3. The Bencoolen
The Bencoolen is ~3km away, just behind the popular Bugis street. You will find 2-3 shops here as well that are selling luxury watches, particularly Rolex, as expected. Singaporeans love Rolex and there is massive demand for such watches, especially Submariner and GMT Master II watches like Batman, Batgirl and Superman.
4. Shoppes at Marina Bay Sands
If you want to buy brand new watch that is not a Rolex, consider visiting Shoppes at Marina Bay Sands. There are exclusive showrooms of Breitling, Richard Mille, Frank Muller, Omega. IWC and Rolex. As expected by Rolex, all watches were display-only and none could be bought. There are cheaper watch brands as well, including Seiko, Rado and Casio. The G-shock store at B2 is amazing.
5. ION Orchard
ION Orchard, like the Shoppes, has stunning array of exclusive watch showrooms. There are few watch boutiques at the entrance that offer many mid- and high- tier brands. There are showrooms by Omega, IWC among many others at the ION Orchard.