This should be the first item to think about as it's the base-bone of your photography choice. Here's what you should be looking for.
- Does the photographer have good quality images (not too dark, too light, orange, etc)?
- Do the photographs have an altered color or over-effecting to them that's not natural or timeless?
- Does the photographer fit the style of what you're looking for (soft and dreamy, loud and fun, funky and sexy, etc)?
- Do all the photographer's weddings have that similar style that you're looking for? You don't want to hire someone who isn't consistent in giving you the quality and style of photos that you're paying for.
- Do you notice wrinkles, blemishes, unattractive angles, awkward poses or distracting backgrounds in the pictures?
- Does the photographer absolutely guarantee that their 2nd photographer at your wedding will provide the same quality of images?
* A good way to see this for yourself is to ask to see an entire proofing gallery and make sure that the quality of photography is consistent throughout like this one of mine.