Ham radio enthusiasts increasingly can't buy/sell equipment on general marketplaces due to regulations. They need a platform that understands their needs.
A classifieds-style marketplace would focus just on amateur radio gear, with proper category filters and verification for legal operation.
Monetize through listing fees and optional promoted listings. The tight-knit community would support a dedicated platform.
Start with basic listings and messaging, then add escrow services.
The risk is low initial liquidity making the platform feel empty.