Client: I want you to make a php script for sending one email with some information of a formulary
Me: ok! it's easy, fast and cheap, if I have the form.
Client: yes, the form is on-line now.
After a couple of hours copy-pasting the code, 've finished the work, the test, and sent the script... Next day
Client: Your code don't work! FIX THIS INMEDIATLY
Me: ops, I'm really sorry, I'have test it on my own web and it works fine, can you show me the configuration of the server?
Client: Look, call here, and FIX IT, they are the server admins (Big Telecomunications giant's HelpDesk).
Two weeks of embarrassing calls after, I discover that client never contracted a PHP server. (this is another quote, but is too long for my english skills)