FCC allows suppliers to self-declare conformance with EMI/EMC rules. You’re obviously taking a risk selling stuff if you haven’t had it properly tested so don’t really know if it passes but it’s unlikely to really be an issue for a small maker selling low quantities, especially if any intentional radiators (Bluetooth, WiFi etc.) are already-certified modules.

Your device tends to need to be causing problems, that the FCC then go and track down, and then come back to you. That is (hopefully, depending on the kind of device) extremely unlikely.

As for Ali stuff, probably lots of it is not tested but still comes with a FCC label - but if it is shipped from overseas, who is going to take responsibility for it? Nobody… So there is nothing they can do except fine the person who bought it if it’s really causing problems (and usually I doubt they’d even do that if the user wasn’t intentionally doing something they shouldn’t have been, they are just told to stop and maybe the device would be seized/ destroyed)