At street markets like Đồng Xuân or Bến Thành, expect to negotiate. Aim for around 50–70% of the first quoted price, with a smile.
Bargaining is a friendly social exchange, not a confrontation. Smile, laugh, walk away once — the seller will often call you back with a better price.
Fixed-price shops, supermarkets, and most cafes do NOT bargain. Look for marked prices; if everything has a tag, just pay it.