Commercial 
I go out on all kinds of service calls. What I enjoy most is residential lockouts. They often require a bit of skill and problem-solving, people are happy to see me when I show up, and I feel a certain sense of accomplishment when I’m finished.
I don’t think I’m giving away a big trade secret when I say that about half the time I go to perform a lockout in a single-family dwelling—a house, that is—I’m able to find an open window. Usually I ask the resident if any windows are unlocked. Invariably the answer is a confident “no”. I always check anyway. In the end, the client either looks chagrined over being proven wrong, or smug in his vindication. I used to ask over the phone before going out on the lockout call whether there were any open windows. I learned my lesson about doing that the time I arrived to discover the client had decided to give the windows one last check after telling me that none were open. That was a wasted trip on a Sunday afternoon.
Sometimes I worry that getting in through a window is like cheating. People call a locksmith and they want to see a show. Opening a window and climbing through it like a burglar isn’t that. On the other hand, most people also just want to get into their homes as quickly as possible, and checking for open windows facilitates that. The lock picks stay in my pocket until all easier methods have failed.
The other night I went on a very late call and started looking around the house for unlocked windows. I found one in back that looked to be a good candidate and the client told me she’d already checked it. That didn’t stop me from pushing at it and seeing it slide open. I understand how she could have made that mistake. It’s all about expectations. A window can be a little bit difficult to open from the outside. If you don’t expect it to be open, you might interpret the little bit of resistance as confirmation that it’s not. Because my expectation when I show up to a job is that there is an easy way in, I don’t give up when a window doesn’t immediately give.
So if you get back from a vacation on which you’ve lost your keys, check your windows before calling for a locksmith. Also, before you leave for that vacation, check to make sure all your windows are secured. Locksmiths aren’t the only ones who know to check for open windows.