Make sure that you schedule a phone call consultation with your photographer! Sure there are plenty of lists on other wedding websites with hundreds of questions to ask, but consider making it more conversational. Ask them about their approach to wedding day photography, what they like about it, what would they say their aesthetic is, etc.
Ask to see a recent (within the last year!) REAL wedding day gallery. Not a destination wedding, not a styled shoot with models, a real actual couple they spent the time with. It's important to ensure you would be happy to receive a gallery-like they are sharing with you.
Check their social media, not only the photos they post but the ones they are tagged in. Look at what others share that is not as curated as a photographer may be.
Remember there are many things that factor into great photos and while yes your photographer is a major part of that it's important to realize if you are booking a photographer who only showcases outdoor weddings and tented receptions, but your venue is a historic church with a ballroom reception the style you like may not be what you get. Opt for a space with lots of options regardless of sunshine or rain on your day.