About once a month my police officer friend is on a task force that, by anonymous tip, goes to residences, knocks on the door, tells the occupants that suspicious illegal activity has been reported, could they come in?...9 times out of 10 they're allowed in with their drug dogs and 9 times out of 10 there are arrests, not always for drugs.
I have a police officer friend who does the same thing every month or so. The task force operating on an anonymous tip goes to the residence and tells the occupants that there is a report that guns are in the area. They ask is they can come for a look. 9 out 10 occupants comply. 6 out of 10 times guns are confiscated.