How can you be sure that there is an actual person at the other end of the chat line?

I can be sure if another person is at the other end of the chat line by going online. It's very straightforward there are no boundaries to chat with an actual person at the other end line of the line. For example, on Facebook you have an option to chat online or chat offline. If they are chatting online, then chat with them. If they are chatting offline, then there is no point in chatting at all.