If and only if you are selling such low quantity like 20/year, here is my work around.
No FCC forms or certifications. When I sell, my devices, still have a serial number, but, I make sure of the following and declare the following:
1. My device is powered by a fully certified enclosed power supply, with certified plugs, If I wired them within a chassis, I verify that that wiring would meet certification if were ever to come to that.
2. On the shipping product and customs declaration, I declare that the contents is a)
'Electronics audio/video/whatever equipment is a sample for evaluation purposes only. Not for resale. No commercial value.'
b) then I still properly state the monetary value of the goods for shipping insurance purposes.
Note that I successfully sold my sample video scalers internationally across the US/Canadian/EU without issue for 3 years using Fedex and UPS. Note that Fedex and UPS usually handled customs and import fees internally at request of the receiving party, though some clients already had their own agents.
3. If something now goes wrong with one of your devices and you hurt someone, EG: some RFI coming out of your device interferes with an emergency health alarm medic bracelet being needed at the time, or your device destroys some property by causing a fire, you are personally liable.
Note that if you are 'not' breaking any FCC emission rules but don't have approval, you haven't done anything wrong, you just cannot say you are FCC approved. If you will be selling to major retail outlets or in quantity, you will need FCC approval as it will be mandatory.
I guess you could say you comply with all FCC RF EMI regulations, but you are not FCC approved. But, I wouldn't temp fate in trying to play this game...