This is a great question because most sellers just go with the first agent they meet with.
The first thing I would do is Google them before I ever meet with them. Look at their website. Is it professional? Look them up on Zillow, Realtor.com, Yelp, etc. to see what people have said about working with them.
If they pass step 1, speak with them and ask them to email you some of their current and past listings. Are they complete and full of details? Informative? Do they use lots of professional photos? Did they label the photos with descriptions? The MLS listing is the primary thing that will sell your home. It should be done very well. Look up the addresses on Zillow as well. Did the agent upload a video walkthrough? That helps more people see the home on Zillow, but many agents don’t do it.
Step 3, I would set up an interview and interview more than 1 agent. First, did they answer your call or call you back quickly. That’s very important. If they don’t return your call quickly, they won’t return the calls of potential buyers, either. Listen to their presentation. Do they arrive on time? Do they come prepared? Have they come with research on your property already? Ask questions like how many homes they’ve sold in your area, how fast they sold them, what they are going to do to market your home, etc. If they plan to use social media to market your home, how big is their following and will they pay for ads? What is their budget for marketing your home. They should be willing to spend some money to get it sold.
Now you have to trust your instincts. Pick an agent who is successful and prepared, and pick one you like. You will be dealing with them quite a bit during the process, and it should be someone you will like to deal with.
Best of luck in your agent search. There are lots of fantastic agents out here. It shouldn't be that hard to find a great one.