Always post two ads simultaneousy (CL)

Even if one of them is a complete "dummy" ad that expects few or no responses. In fact, make one purposely bad and post it along with your legitimate ad. This will allow you to easily recognize the bots that automatically respond to every single post. When you see two responses in your mailbox that look identical, you can be certain that no one ever actually read what you posted and you can just hit the "This is Spam" button.