You simply tell them you are unavailable. You are not obligated to host a constant stream of people or to accept a guest at a time that is not acceptable to you. The idea is that the network will grow to offer many options in each locale, and that most of us will find something available where we are needing it. AND, we can all help to build the network by spreading the word to friends and acquaintances, and through whatever means we have, so that the network grows to benefit us all.