Many members access their emails only periodically and it may be few days before they reply to your message so it may just be a matter of waiting a little longer.
There are some others unfortunately, despite our best efforts, who do ignore messages and there is not much we can do about it I'm afraid.
Just so you know, every message notification home owners receive has 'house sitting etiquette' information which instructs them to respond to messages and remove their ad if they have found a sitter. The notifications contain a short version of the message so that a member has to visit the website to read the full message and when on the site there is a 'Notice' at the top telling them they have a message they need to respond to. The only way it will go away is if they reply to the message.
When on the website, to make it easy for members to reply, we created 'Standard responses' where all that's needed is to choose a response and click 'reply', there is no need to compose a reply. Lastly we made it so all members can tell if their messages have been read by the other party so even if the other party doesn't reply you can see if they have read your message. You can see the 'read' or 'not read yet' notice under the date and time of the message.