There's nothing automatically wrong with all Singaporean sellers but you need to be very careful about two main things:
1. It is a very humid country and watch movements can suffer badly over decades of exposure to that climate, as can dials
This leads to
2. A lot of redials and a lot of revamped movements. Unfortunately most watches on the market have not been well done in either respect, so there is a very high proportion of watches with terrible redials and butchered movements.