I agreed most on this one:
4 On looking at sketches or concepts: "Well, we aren't sure if we want to use you yet, but leave your material here so I can talk to my partner/investor/wife/clergy."You can be sure that 15 minutes after you leave he will be on the phone to other designers, now with concepts in hand, asking for price quotes. When you call back you will be informed that your prices were too high and Joe Blow Design/Illustration will be doing the job. Why shouldn't they be cheaper? You just gave them hours of free consulting work! Until you have a deal, LEAVE NOTHING CREATIVE at the clients office.

quite a real life situation and many didn't notice the risk before.