First, she had no guarantee. What does that mean? You are taking all the risk if you decide to get your photos done by her studio. Whatever the cost, you will not get your money back regardless of how the photos turn out. She also hires assistant photographers, so she may not be the one who photographs you.
According to the Yelp reviews, there were several people who were very dissatisfied with the results, to the point they did not want to share them with anyone; they didn't receive what they had wanted. There were also many happy clients, but what if you are one of the dissatisfied ones? The photographer may be very nice, personable, and friendly (as this one was), but if they don't back up their work with a guarantee, and the photos are no good, that won't help you.
What should a guarantee include? Two things - a free re-shoot if you are not satisfied with the results, and if you're still not happy, then all your money back that was paid to the photographer (every penny, including any deposit). Note: Hair and make-up may be separate, so you may need to negotiate with that person for a refund. Or you may want to schedule your session in the late afternoon, then go out for a night on the town afterwards (because you'll be looking so great) - that way, the hair and make-up will be put to good use either way.
Second, check out the photographer's portfolio and see if you like his/her work. Keep in mind that most people will show you their best work. So if their portfolio doesn't look good, you know it's time to move on.
Third, how much time will they spend with you? This includes meeting with you before the day of the session to answer all your questions and offer suggestions (such as what to wear, how many changes of clothing, poses you might like, what your photos are for, what do you like best about how you look, etc.). The more the photographer knows about what you want, the better your photos will be.
Fourth, if reviews are available, check them. Also testimonials, although they won't post them from unhappy clients, so they are a bit limited in value.
Fifth, always, always meet with the photographer before scheduling a session. You have to make sure you feel comfortable with them.
I'm sure there are more things to consider, but this was off the top of my head. Hope this helps.
