I almost never go to flea markets in Singapore anymore because there's never good stuff to buy. A flea market is where you buy relatively good shit on the cheap - not your worn Forever 21 dress for $20. I went to the Brooklyn Flea Market bright and early on a Saturday and scored two vintage dresses for $5 each, and a vintage money clip for my brother.
On that note, while I complain about how expensive people sell stuff at flea markets, I also get very annoyed when people complain about how incredibly marked up vintage stores are in Singapore. On one hand, as someone who loves vintage pieces who've shopped overseas for them, I understand where these people are coming from. But on the other hand, a lot of customers forget that vintage is hardly ever sourced from within this island unless you want to wear your grandmomma's kebaya. Buying trips cost money; plus, if it's a brick and mortar store - there's heaps of overheads to think about and taken into account.
So before you go on a rampage about how expensive vintage clothes are in Singapore, shut it and go buy it cheap on eBay instead.