I contacted Sigma about 6 months ago and asked what they needed for coverage. They told me that I needed to have the receipt even if it was registered. I asked about gifts and they said that they only honor repairs with the warranty. Now, they did not tell me that a gift had to be a brand new lens, so I don’t see how the name on the receipt will make any difference at all.
Maybe you bought the cheap filter attached to the lens and he gave you the lens as a gift for overpaying for the filter?
Yup this is what I think as well. And this is probably one of the reasons they never ask about the original owner.
Anyway, I just picked it up and guess what!! I have won the lottery - it focuses fine 


