What if the police go a step further and start offering money to criminals to allow searches. Soon, you'll see people choosing to get busted in order to get an FBI payday, while the FBI can tout their high closed case rate.
But there's still confusion in the courts about the difference between physical and virtual property and the peoples' rights to escape search (using radar through walls or taps on data feeds). This malign overreach of prosecutors relies on that.
But I think this practice clearly crosses the line since the property is physically in the hands of an untrusted party. It'd be trivial for Joe Schmo at Best Buy to plant evidence. Because that possibility is so plausible, this chain of evidence has been compromised. Any appeals court would toss this practice as unlawful, IMHO.
That's actually legal. The catch is they can only search the areas of the home the roommate "controls", meaning anything they find in a shared space like the bathroom or kitchen is legal, but your roommate can't consent to a search of your bedroom if that's understood to be your space.
I think it gets dicey if you left the bedroom door open and they can see evidence of a crime from the hallway.
If your wife or live-in girlfriend consents to a search the entire place is fair game, though if your wife is willing to sell you out for fifty bucks you have more than one set of problems.