The dividing line is visible if you know where to look: informal venues negotiate, formal ones do not. Firmly in bargaining territory across most of Asia, Africa, the Middle East, and Latin America: open-air markets, bazaars and souks, street vendors, souvenir and craft stalls, and unmetered taxis or rickshaws, where the fare must be agreed before you get in, that last part being the single most useful rule in this entire subject. Antique shops, carpet shops, and independent stores in tourist zones usually expect negotiation too, and even mid-range shops in some countries will offer a discount if you politely ask.
Fixed-price territory everywhere: supermarkets, chain stores, malls, pharmacies, restaurants, cafes, hotels with published rates, and anything government-run, along with metered taxis and app-based rides, which have largely replaced fare-haggling in cities worldwide and are worth defaulting to for that reason. In Europe, North America, Japan, and similar markets, assume fixed prices in nearly all retail, reserving negotiation for flea markets, big purchases, and rent.
The quick field test when unsure: printed price tags and barcode scanners signal fixed prices, while unmarked goods and a vendor who sizes you up before quoting signal negotiation. And a soft opening, simply asking whether that is the best price, is polite everywhere; the reaction tells you which rules apply without any risk of offence.