Anyone can buy a saxaphone, but it takes lots of practice to learn how to play it. The same holds true for photography. With better and better cameras hitting the market every year, accessibility to great technology is reaching more and more people. Knowing how to use that technology is what truly makes a professional picture.
Below you'll see two photographs taken within seconds of each other. The first is the intended professional picture. The second is a standard shot taken on default camera settings.
You can see above that detail has been retained in the background. The sky is a deep blue and each cloud is defined. The "exposure" is set for the background to give the image more depth. A secondary side flash is then used to highlight the subjects giving a perfect second exposure to light them with perfect skin-tone.
This image is what an average photographer would get shooting to balance the exposure between the background and subjects. You'll notice the background is more blown-out white and the subjects are more in shadow. The sky isn't the deep blue anymore and all colors seem muted.
If you're shopping for a photographer - these are the things you look for. Obviously you want to look at prices, package offerings, album styles, etc - but when it really comes down to it, the quality of the image is what you're hiring a professional photographer for. Being able to handle any lighting scenario and get a great image is what separates a professional from someone who just went out and bought a really cool camera.
Hope this helps! :)
