Matthew Baldwin has compiled an excellent list of trade secrets and techniques that are otherwise known only to the professionals or employees. Here are some favorite "Tricks of the Trade" for the tech professionals:
Graphic Designer
If you have a client who is unable to approve a proposed design without putting her stamp on it, just put an obvious error in the proposal: a logo that's too large, a font that's too small, or a few judiciously seeded typos. The client requests the change and feels she's done her part - and your design, which was perfect all along, sails through to approval.
Technical Support
When helping someone fix their computer over the phone, and you want them to see if all the cables are plugged in correctly, don’t ask, "Have you checked to see if the cable is plugged in?" because the customer will always say, "Of course I did, do you think I’m a moron?" Instead say, "Remove the cable, blow the dust out of the connector, and plug it back in." The customer will most likely reply, "Hey, it’s working now - I guess that dust really builds up in there!"
Source: The Morning News, Tricks of the Trade [via]