There's no way to tell.
2 years ago in my town there was a bust where over 100 people got taken down by an undercover.
The guy was a fucking LUNATIC. I'm not kidding. He was this crazy ass, hardcore gangster type with prison tats and an attitude to match. He got deep into the local scene and no one suspected for a minute that he was an undercover... He almost singlehandedly brought 80% of the drug trade in the county to a screeching halt for over a year before anyone had the balls to step in and fill the void.
He got in fights, did lines with people, fucked the locals' girlfriends, you name it. The worst anyone thought was that he was part of a gang trying to extend their power from a nearby city. But never in a million years that he was a cop. OOOOPS!
Big mistake.
One more reason I will NEVER NEVER deal.
Grow your own.
That's the only way to be sure.