There are different grades of GPS receivers, all licensed differently. Consumer-grade receivers have a maximum accuracy of something like 3 meters and a slow response time. There are also aviation grade and military grade receivers, which cost more (build & calibration) but also require a special license.
I interned at Trimble in the radio group. Industrial GPS receivers could be purchased by more / less anyone, however they were built and priced for heavy-duty industrial consumption (mines, farms, ships, aircraft, etc.). The unassisted accuracy without kinematic corrections was around +- 1 m horizonal and ~10 m vertical, constantly changing as the constellation moves. This would be for a top-of-the-line 24 channel parallel receiver. WITH kinematic GPS, +- 10 mm (not a typo) horizonal and ~3 m vertical. It was so good that receivers could be installed on the left and right sides of a grader's blade that the angle and position could be known with great accuracy and precision. Kinematic means a nearby stationary reference ground base station sending updates over radio frequencies to another GPS receiver that could be in motion. This was also used to subtract SA pre-Clinton because the injected error would be the same in nearby locations.
