I've read thru literally dozens of forum threads in other forums about folks buying an iPhone from Craig's list or from some other advertisement only to find out later the phone had been stolen. Once the imei is blacklisted, the phone is worthless. If the price and/or deal is too good to be true, avoid it like the plague.
On one level, that's absolutely true. A blacklisted phone is just a paperweight.
Unfortunately, on another, it's absolutely untrue. I wish your last paragraph could be pinned to the forehead of everyone who gets burned as a result of believing that iCloud lock can be circumvented. It can't.
The stolen, blacklisted, locked phone DOES have value. Once the thief has it in his hands, he only has to find a gullible or uninformed mark and he is several hundred dollars better off.
It's at about this point that the uninformed new owner hunts down forums and learns, too late, that they just got ripped off. And now the phone IS worthless, because people who fall for the scam are not the kind who will simply readvertise it and pass on their error.
We are conditioned to believe that crime doesn't pay, and it's comforting to believe that. Unfortunately, that isn't true either.