Blacklisted me that the ESN or IMEI of the phone (the phone's ID to the Network carriers), has been banned, due to non payment, being reported lost or stolen. What this does is once the number get reported, all carriers will not activate that particular phone, until the reason it was blacklisted is cleared up, which is most often NEVER.
Sound a blacklisted phone be avoided? YES, because you can't use it for its intended purpose. Is it a rip off? Only to the person looking for a deal, from a slick talker, who tells them all they have to do is get this or that done to the phone to make it work. If it was that easy the seller would do it and sell it for more money.
So if you think you will be buying a normally $600+ phone for $150 bucks, you are mistaken and wasting your money. Unlocking the phone will not help, nor will jailbreaking. So if you still buy such a phone, knowing ahead of time that you are basically scamming yourself out of the money you'd be paying for it, the only person you'd need to kill, would be yourself, for being an dummy, that thought he was smarter than those that were telling him NOT to do it.