Originally Posted by
failedtaper 
When I was going to meetings years ago, I always avoided parking behind this particular building the meetings were housed in because of the drug deals going on in the back. Dealers there knew who was at the meeting, and the folks who were forced to be there against their will were often the ones in the parking lot making the deals.
It is generally common knowledge among active drug users that when in a new town without a suitable connection, this is one way to find one. There was even a depiction of this in the show "Breaking Bad" from AMC, so one may reasonably conclude that many in the general population, and certainly the police, know this as well.