> How does a raid only target people who are here illegally? How do agents determine the identity and status of the person they're grabbing in a factory or school?

This has been done for decades and has very established standard operating procedures. Do you think immigration raids started with Trump? This has been going on since the 1950s and there is established legal basis and agency procedures specifying exactly what the agents can and can't do, along with repeatable methods for verifying identity and legal status.