I've always been a bit befuddled by how much to tip the person who brings my dinner I order through room service at a hotel.

On the menu it usually states there is an 18% service charge (or another figure similar to that) along with a $2.50 delivery charge (or other type of fee) in addition to the cost of my food.

Do those extra fees/charges include a tip for the server? They don't specifically say gratuity, so I'm never very sure. On one occasion, I tried asking the person on the phone when I placed my order, and they were very hesitant to answer the question and gave a very vague answer (which I don't recall exactly, but I do remember hanging up and feeling not really sure what the answer to my question was).

So, in the absence of not really knowing, I usually end up tipping 15 - 20% of the cost of my food.

Am I being scammed? Is the server getting tipped twice if I do that?

Thanks for your input and guidance.