I used them once a very long time back when the first appeared on the internet, I paid a premium price for an Intel pentium processor which was said to be tested and guaranteed to be overclockable, it came in a box with the seal broken but when fitted into the motherboard and booted up it opened with an Intel splash screen announcing something like "Welcome to the first bootup of your new Intel processor"
His PC came today like he paid for. But they havnt fitted his graphic cards. He seems to have all the boxes and paperwork he should have. I have left him in his room fitting the graphic cards wiill let you all know how it goes.