You can't get through immigration without a sticker. You can't get the sticker without paying for it. I think that if tax was included on the ticket that it's a different tax or a mistake. None of my tickets have a Peruvian tax liability that I can see.

Santiago is a funny one, though. Absolutely make sure that the tax is there. They *will* check it, and it's more expensive to pay at the airport. I love Chile and I love the Chileans, but they are some of the most anal retentive people about certain things. I have had to pay twice for Chile at one point when the tax line was too long for the ticket and they omitted the Chilean tax from it.

Also, I think a lot of S/A countries have several different types of taxes, from my understanding. Some are charged against the ticket, some are charged at the airport. Not double charging, but rather collecting in two different places, I guess. Venezuela is another one that is funny about that.