So, it seems that sooner or later every designer has to deal with the worse rite of initiation of being burned by a client. It seems to happen a bit more when you're freelancing, but having a "client" not pay you for the service you provided sucks. They will dodge your phonecalls and e-mails and you're only trying to get paid for what you deserve. It usually happens when you're starting out, but sometimes it'll happen to a vet. I came across this article and thought it was a great article on how to get clients to pay. It even lists how you should handle your business with friends and friends of friends, which I think is very important. Pretty much, never be lenient with them at all.
To read the article: