This type of activity isn't limited to major metro cities -- it's happening (with surprisingly frequency) in the midwest. Cincinnat/Hamilton County is notorious for doing this type of thing, but instead of with Methadone, it's with Suboxone; it's a drug that blocks the detoxification effects of heroin.

The police are under pressure to make more Heroin arrests -- so much so that they're targeting people who may or may not have a criminal history and asking them if they know anyone who has some Heroin for sale -- and offering to give them up to $500 if they do. For most residents of Hamilton county, $500 is a fair amount of money....and they always 'know' someone who 'knows' someone who can supply the drug...so they'll say yes (and then get arrested for trafficking).

This really boils down to a lack of good mental health and health care. I have two friends who are struggling with a Heroin addiction -- one fell off of a roof while working, and the other just can't cope with her problems; if we had better and more affordable health care (and while I support the ACA 100%, I still think we need to move to single payer healthcare), I don't think either of them would be addicted to the drug now.