the Secure and Trusted Communications Networks Act of 2019 (47 USC 154 1601 ff) is one place, among others, that Congress gave the FCC the authority to make rules about importing and selling electronics
(b) Restrictions
No person shall manufacture, import, sell, offer for sale, or ship devices or home electronic equipment and systems, or use devices, which fail to comply with regulations promulgated pursuant to this section.
It sounds like it will be up to the courts in this case to determine if these specific FCC regulations are actually made pursuant to the purpose of that section, and whether operating a marketplace within which others are offering radio equipment for sale can be interpreted as you yourself offering that equipment for sale.
The 2021 and 2019 laws are relevant because the FCC said they expanded the FCC “authorization power” in 47 usc 302a to include covered entities and national security threats, not just regulation over electromagnetic compatibility issues