See full galleries.
Ask to see full galleries, no photographer should hesitate to show off their work to you. Specifically ask to see a gallery that shows a similar length of coverage to what you're seeking, and if at all possible something that shows a similar environment. IE: Are you having a barn wedding in dark barn - ask for something similar. This will show you they're capable of shooting in your chosen environment.
Sign a contract.
Despite common belief, contracts are not that scary. They're just outlines of an agreement you're participating in. They're there to protect you AND your photographer, they serve to protect you both. Do not give a photographer, or any vendor, your hard earned cash without a contract in place. Read that contract, ask any questions you have and make sure you understand it before you sign it.
Is there a backup plan?
What if your photographer breaks their wrist hiking for an elopement the weekend before your wedding? Do they have a plan? What is it and do you know it too?
Read their google reviews.
What do other people say about them? This will give you insight on not just their work but HOW they show up for their clients (or not). This is important to look for.
If at all possible, meet them.
It's not always possible, so this one is a bonus. If you can meet them in person do it! Go grab a snack and sign the contract in person even. If you can't meet in person (for whatever reasons) try to get them on zoom, skype, or even a phone call to make sure their energy matches yours. Most photographers will want to suss you out too.
Do the Engagement Session!
We're of the opinion you need to like your photographers or you're not going to like them chasing you around all day for your wedding. One surefire way to determine if you like someone is to spend some time with them. We recommend booking an engagement session before booking them if you're unsure.