Fingerprints
When I went to the US recently for a rating I got my fingerprints taken at the local airport on arrival where there was a TSA office. Their role was providing ID checking facilities to the airport workers.
They charged $36 for the privilege and needed passport/ID plus a completed form and the correct part of the email that is sent from the TSA alien flight training system that permits you to have your prints taken.
The big advantage was that they have an electronic scanner that both ensures there are no quality problems and also transmits the prints direct to TSA HQ. That meant I got a result back in two days.
You can go elsewhere but the other places I looked at charged varying higher fees as a result I believe of a $74 processing fee levied on outside contractors.
You can also have the prints taken at the local sherriff's office. It would no doubt help if theye were friendly but usually thgese are paper and so there is a no doubt significant delay in processing.
One item to watch out is that the TSA ID offices are open varying and, acccording to how busy the airport is, limited hours.