Also look for consistency in their work. This is a way to differentiate an amateur from a professional. An amateur photographer’s portfolio may show nice images, but those images are a compilation of one or two accidentally good images from many sessions. The professional will show quality images consistently in both their portfolio AND recent work on their blog. If you hire an amateur to shoot your session, you accept the risk that there may only be one or two good images from your session vs. the 20-30 great images that a professional will provide in your gallery. When you hire with quality in mind, you buy the assurance and the peace of mind that your special moment is captured perfectly before it is lost in time.
Also, check if there's a second shooter included in the contract, and if there's not, ask about the possibility. It's likely the second shooter can be confirmed later on, but the main benefit to having two shooters is, of course, you get twice as much coverage. For example, during your formal photo session, one photographer can capture the formal photos, while the second one can get behind-the-scenes, photojournalistic photos, like your guests mingling. If you're having a larger wedding (250 guests or more), you might even want to ask about having three shooters so your photography team can be sure to capture the event from all angles.
When styling a photo session, I like to start out with a basic color palette and go from there. It can help to have one “rock star” in the photos who carries a pattern in their outfit that the rest of the group’s clothing or accessories pulls from, while keeping everyone else’s outfits more simple. You can do this with a neutral and a few colorful brights, or try a softer palette that has different tonal ranges of the same shades.