How much would it affect the price of an HDB/Condo unit if someone dies in the flat or the couple of the flat divorced?

If the couple divorce, it will depend on if they are in a hurry to sell the flat. If they want to get rid of it fast, you can negotiate with them or their agents for a slightly lower price. I’m pretty sure divorce is considered personal and not required to be informed to potential buyers.

If you are thinking of Feng Shui, ie unluckiness, doubt it’ll make much of a difference. P/s if it’s every couple that stays there, will break in 1-2 years then maybe there’s an impact after some time? Only can find out if you speak to nosy... I mean friendly neighbours.

For death. Seriously no idea. It might turn some people off. But I doubt it will drop to the level like Hong Kong.

But this brings up an interesting question. Are the owners or agent obliged by Singapore law to tell potential buyers if a death (whether natural or not) has occurred in the house? I’ve only read of this requirement for the US and HK.

Most of the time, such information won't be obvious. (unless it's a big media news) so the selling price does not get affected.

In those sensational stories blown up by the media, flat prices definitely will drop but after a few months of quietness, no one will remember much. a 5% difference from market price will get it sold quickly.

This is land-scarce Singapore after all