Answer:
There might be a passage attached but from a general perspective, tourists usually have an advantage in bargaining for souvenirs because they are the only market being sold to. Souvenirs are usually made exclusively for tourists which gives them bargaining power because if the tourists do not buy the goods, no one else will. The number of locals who will buy souvenirs from other locals is statistically insignificant because the locals make the souvenirs themselves.
When they go into the town or city of Angoram, you find that the shops there are selling to many more buyers and so the prices are set and cannot be bargained. This is why the locals cannot ask for 2nd or 3rd prices.