SOP where I come from.
Depends on the location.
In my hometown of 2000 I might let them in but that's because I know them personally.
In ANY large city in this nation I wouldn't let a policeman into my house without a warrant stating specifically what they were looking for and would want an independent witness to go with them.
Might not be possible but that's what I would want.
Heh, about 20 years ago there was a part of Portland, Or. called St. Johns. There was a house there that was a biker gang house. They were involved in a rolling biker war with some other gang so they had barricaded the ground level doors and windows with furniture and plywood.
Anyway, one day someone is trying to bust down the front door at 4am so one of the girls inside calls the police while the guys grab shotguns and pistols. The guy outside is able to kick the front door in partially and the bikers see no uniform so they blast him. They ended up having a 10 minute gunbattle with the people outside. They turn out to be police officers. The one attempting entry was killed and several others wounded.
After the smoke cleared there was a big investigation and the only drugs found were in the jacket pocket of the plainclothes officer that was initially trying to enter the house. It caused a big stink at the time. Of course, the bikers had plenty of time to dispose of any evidence they might have had, but still…
Dude, I think you are just a tad naive....