Remember, in the US, you can be charged for obstructing a plain-clothes officer's duties even before they ID themselves. (I'm not a lawyer but you could refer to 18 USC 111 or 18 USC 1501, or the fact that police don't need to know the law properly to enforce it, Heien v. North Carolina)

And, fake-ICE cosplayers like this guy can have their charges dropped by DOJ or pardoned by Trump.

So if you get visited by someone unknown, you're damned if you do or you don't. Demand a judicial warrant and wait to receive one with an actual judge's signature, before you open the door to agents you don't know.