Ask the agency to provide you with a copy of the fee schedules for various services, including any costs related to an adoption that may be charged by others. Get a copy of the agencies' written policy on refunds. Ask for a copy of the agencies' most recent annual report, their most recent outside audited financial statement and the names of some clients in your area with whom they are working or with whom they have worked. Review the information and talk to those individuals about the agency. Ask friends who have adopted about their experience with agencies.
Word of mouth is the best advertisement, positive and negative.
NCFA or other national membership organizations typically have, on their membership rosters, agencies which vary substantially in their quality, but they do not rank them. Ultimately, choosing an agency will have less risk if you have gone through the steps above and been alert for indirect or even silent signals that there may be problems with that agency. Close friends whom you trust may often be able to get you candid reports that you cannot obtain yourself. Be aware that despite well-publicized accounts of agencies that failed to perform as advertised, this occurs relatively infrequently in the adoption world. On the whole, adoption agencies do a good job, are staffed by honest and sincere people, and have boards of directors who take their responsibilities seriously.