Peruvian hotel taxes.

I have several reservations through Marriott. There is a 10% tax. And there is an additional 18% tax for Peruvian residents and for non-residents who have been in Peru for 60 consecutive days (per the Marriott site).

My property states that my reservation cost does not include 18% for "some extras just in case you will have". Is this a scam (I dislike that word) to collect 18% that the property is not otherwise entitled?

For a point of reference, I tried a reservation through IHG, and there is a reference to 10% & 18% (not to mention another 10% service charge). No mention of the 18% only being for Peruvian residents/60 consecutive days.

So, which is it?

Many thanks!