[Gogar]

Most Room Service charges include a set fee "delivery charge" + usually 18-20% "service charge" or "gratuity" automatically.

I don't usually order room service, but if I do, I don't tip above the set included service fee unless the service is above and beyond. If you get a burger, and there's no ketchup when the guy brings it up, and then he runs down and grabs you some and brings it back 2 minutes later, heck yeah that's worth a couple bucks. But if they knock on your door and throw a cold plate of french fries at you, then no way.