They are now other sites claiming to unlock your Mac with the Hash Code, do not be fooled, they will take you money and never send you the code or send you the wrong code and it will corrupt your EFI Chip and Logic Board. Only Apple can unlock your Mac with the Hash Code, No one else. If you attempt to put a wrong code in, you will corrupt you EFI Chip and Logic Board. Once this happens, they is no way to fix it.
WARNING!!! Do not try and unlock your Mac on your own or by using other processes (Removing EFI Chip, Unlocking with Hash Codes, Etc). It will corrupt the EFI Chip / Logic Board making your Mac an expensive paper weight. It can NOT be fixed, it is permanent.
There have been a lot of people selling Mac computers on eBay and Craigslist that appear to be working fine. But as soon as you buy it, they will lock it through iCloud. Once your Mac is locked, you will try and contact the seller (If you still have their contact info) but will not answer or reply. So then you will take it to Apple for them to unlock it just to find out it is reported stolen and have Apple take your Mac so that they can give it back to the seller that sold it to you. Now that you just lost all your hard earned money, the seller will go and sell the Mac again to someone else and do the same scam.