Asking as a complete amateur, how do these people databases & privacy companies work? They claim to get personal details, family connections, social media content and even court records etc for not-so-exhorbitant price ($30 per report as ballpark?)

Do they just scam people by compiling whatever is available on search engines? In one or two cases, I have seen them at least giving the house address or family member details right. So there seems to be more at play.