Missouri Law :(please check for changes)
451.100. Marriages may be solemnized by any clergyman, either active or retired, who is in good standing with any church or synagogue in this state. Marriages may also be solemnized, without compensation, by any judge, including a municipal judge. Marriages may also be solemnized by a religious society, religious institution, or religious organization of this state, according to the regulations and customs of the society, institution or organization, when either party to the marriage to be solemnized is a member of such society, institution or organization.In some cases there may be additional requirements, such as a:
- Statement of Good Standing or a Letter of Congregational Authorization.
- Official document showing the person is Ordained.
- ID - Your minister should have an ID from the organization that they were ordained through and a picture ID such as a Driver's Licenses or State ID.
You should ask to see these documents for your own peace of mind.
I am not an attorney and can not offer any legal advice, but here are some websites you may want to check out.