Complete Memory Loss

One more reason to make sure you have a contract before proceeding.  It's not uncommon to be asked to do additional work before a proper agreement is in place by someone who urgently needs your help and assures you that "We'll take care of the paperwork later".  ...And it's also not that uncommon for selective amnesia to strike that person after you've solved their problem and they no longer need you.  If you've been burned by this scenario more than a few times, perhaps it's you who needs his head examined.