Choose an attorney with experience in private adoptions. When you interview attorneys, ask if they are a member of the American Academy of Adoption Attorneys or an equivalent state accreditation. If your attorney is not accredited, question her about her specific experience handling private adoptions. The AAAA maintains a directory of accredited adoption attorneys in the United States.
One point that Matt mentioned that I found interesting, and certainly gives the service credibility, is that they have lawyers that use their service as well. The lawyer will sell the service to a client for thousands of dollars and then pay RapidAdoption.com to prepare the paperwork for them. There are some that they work with regularly and have an agreement with and some that just purchase the service from their website and give the paperwork to their clients as if they had done it.