Compared across countries

Can you haggle over prices?

For a trip that crosses borders — the same question, answered country by country.

The pattern

The printed tag is the dividing line. Where one hangs the number is fixed — in China and Thailand that is the law rather than the custom — and where none hangs, the first number is an opening position. Japan is the outlier: it has no side where the number is soft.

Japan

No. The marked price is the price, and asking for a discount will be met with polite confusion.
China

Not where a price tag hangs — marked prices are a legal requirement, and the tag is a ceiling. Markets without tags are a different world.
Thailand

At markets and stalls, yes. Where a price is displayed it is not a starting point — displaying it is a legal duty, and the government's own advice draws the line in the same place: prices run higher for foreigners "outside of regular shops that have fixed prices".
Vietnam

In markets and casual shops, yes — the tourism board's own word for it is gentle negotiation. Ask a few vendors first so you know what the number should be.
South Korea

Only in traditional markets, and only gently. Everywhere else the price is fixed and asking reads as odd.

Sort the practical stuff before you fly.