There comes a time when your brick wall is truly a brick wall and you have exhausted all known methods of obtaining data on a particular person or family. Perhaps it is now time to turn to a professional for help.
First would be a need for someone in a U.S. town, county or state because it is inconvenient for you to travel there. There are several possibilities in this case. The first would be a volunteer who might be found either on the Internet or by calling the local library, genealogical or historical society. This person may or may not wish to be paid since some own a hard to find book which may help or (s)he may refer you to another with greater knowledge.
Second might be help a writer might offer from his research and books. The one with which I am most familiar and who has written many books on Maryland families and records for example is:
Barnes, Robert W. Baltimore County Families- 1659-1759
Barnes, Robert W. Maryland Marriages 1634-1777
Barnes, Robert W. Maryland Marriages 1778-1800
I and a cousin hired him, and though he was unable to help on our particular problem, still he provided a useful review of data available.
Lastly would be one who offers research efforts for a fee. Here you need to be careful with open-ended searches. Restrict and announce the amount you are willing to spend and how you wish it to be accounted for.
To be safe you should hire a person who is a member of the Association of Professional Genealogists (APG), or whop has been certified by the Board for Certification of Genealogists (BCG). Both sign a code of ethics and offer mediation services for disputes.