It is not a good idea to approach any celebrants direct if you don't eye-witness their performance during wedding ceremonies.
Although you may find out how they look and speak by going to their office for no-obligation meetings, you can never tell what their live performance during wedding ceremonies will be.
You may seek referrals from your peers. However, unless they are in wedding-related businesses, their knowledge and experience in wedding ceremonies are very limited. In that case, they are no better than you yourself to tell whether a celebrant is as good as you expect. Their referrals can utmost give you the names of celebrants.