Thanks for all the replies and for making this a new, updated thread.

So just to clarify in my case, I am talking about the Peru International Departure tax of US$31 per passenger, not the domestic taxes. I booked a flight using miles that included a LAN flight from LIM-EZE and was told by AA over the phone that all Peru taxes were included in the taxes I paid upon ticketing. Then at check-in at LIM, LAN told me they couldn't give me the "taxes paid" sticker because "AA is the only carrier that includes the tax in the prepaid taxes on the ticket", so I was directed to the AA desk. After waiting 3 hours for them to open, they told me the tax was in fact NOT included; if it had been they have a roll of "taxes paid" stickers right there on the ticket agents' desk and they would have stuck it to my BP.

So the mystery is why normally AA includes the tax but in my case it didn't. I paid over $350 in taxes when this trip was ticketed so...? Was it because the flight was actually a LAN flight?? No one at AA can give me a straight answer and while it isn't a ton of money, I hate paying taxes twice. And it has kind of shaken my confidence in the knowledge of AA in Latin America, which I thought was their best territory. If the typical AAgent is as clueless about LatAm departure taxes as the ones I've been getting, that's pretty sad.