The best marketing is word of mouth.
And it is the cheapest.
Many Guest today have their own Travel Blog, are active on Facebook and other social sites. They , as well as the Marketers mentioned above, Have a vast network, compared to Guest of 10 yrs ago.
Keep your Guest happy and many new guest will tell you they heard of you from "My Friend".
It compounds quickly these days and a referal from a friend is trusted more than anything else.