Keeping good records is what it is all about.  I love email since it provides the ability to chronologicaly document the situation.  Online phone records can be very useful in proving time and duration of phone calls, even if the receiver contests the content of the conversation.  Text messages, while less used in business, can be easily documented.  Instant Messaging is becoming common in business for instant, easy and cheap communication, so making sure you have the right software to copy it, can be important too.