The casting director is going to have many people put in front of him/her that all basically look the same or very similar.  Sure your skills are something they look for, but more importantly, they are seeking great personalities that are easy to work with.  Think of your audition as a job interview.  You want to leave the best possible impression so that you will get a chance to a second interview to secure the job.  However, it is not a social club.  You don’t want to be over the top personal with the casting agents.  Be yourself, smile warmly and don’t be afraid to make eye contact.  If they enjoy being around you, that is a good indicator the director of the show, commercial or movie will also enjoy working with you.