The PIN is a legitimate security feature; Apple can remedy a Mac that is locked, you either need to prove proof of ownership or replace the Logicboard. Frequently we see such post`s, the most likely individuals to benefit from a step by step unlocking guide are those that have ill intention, or those who happened to pickup a $2K notebook for a few hundred dollars.
I have no doubt a small minority do fall "between the cracks" equally the present system protects by far the vast majority of honest owners. I have read so many posts attempting to justify reason for unlocking the PIN; I forgot it, if we crack the PIN it will force Apple to strengthen the system, I bought a used Mac and it was locked remotely, I want to test the system. Bottom line is those most likely to benefit are thieves, plain and simple common sense.
If you plan to buy a used Mac, buy it from a reputable source, a family member, a friend, a colleague, a known vendor. The guy in the car park wanting $500, for a new Retina is none of the above. I have been around Mac`s a long time, know a lot of people who own Mac`s and businesses that use Mac`s and to date I have never heard or seen a Mac locked by some fault of the system.
As for those that inadvertently remotely lock their Mac`s, all I can say is there are plenty of warnings. I know it sucks, equally it`s a consequence of your own actions. Personally I hope Apple move off the 4 digit pin to something more complex, as I am sure that there are many who will happily sit down and work their way through the 10K permutations for a free Mac
