The world market prices for primary commodities, such as iron ore and steel, are maintained at an artificially low level in order to inflate national export trade against competitors. This is possible because primary resources are treated as unlimited, low value goods in an international market with heavy competition between countries.
External costs are a major reason that price signals are unreliable. A good example is the price of gasoline, which in the USA carries a social cost of at least $4.00 a gallon but is sold to Americans for $1.20. Another source of unreliable price signals is perverse government subsidies.