Originally Posted by
iknowthings
I may have misunderstood your first post. I think I understand it a little bit more clearly after this clarification.
Extra guest fees are usually disclosed in a bright blue box at the top of the screen when you're making the reservation. If the fee was implemented after the original booking of your reservation, it is likely that you can get it waived.
The Lurker responded to you so let her look at everything and make sure it's all legit.
Sorry for any confusion! Re-reading my OP, I can see how it could've been misunderstood; I'll edit my post to make it clearer.
And thanks for pointing out what usually happens. In my case, there was no disclosure and the fee was implemented after my original booking. I'll follow up with Marriott as per the Lurker's suggestion.