In a word: Lighting. On location I use off camera lighting. Photographs are all about light and the quality use of it. Using off camera lighting enables me to supplement the available or ambient light to create the kind of images you want. The result is photographs that make you say WOW, puts lights in the eyes and separates the subject from the background.
Why don’t all photographer’s use off camera Flash?
Frankly, and Honestly, they don’t know how. It’s a difficult skill to learn correctly; one that is easily done incorrectly, yielding that flashy look. It requires a considerable investment of money, time and equipment and often requires an assistant, so, they bill themselves as “Natural Light” photographers, turning a negative into a positive.
We've all seen those photographs that just look flat!
BTW, if your photographer has the flash mounted on top of the camera, don't walk away....Run, unless you like the DMV look.