I don't blame you. I tried buying one off someone and it turned out to be region locked. They had a USA flag on their Steam Profile so I took that to mean they were in the same region as me in Canada. Turns out they bought it off someone else in the UK and were re-reselling it... fml. I ended up stuck with a UK key so I went down my list until I found someone who had it wishlisted and were from that region and gave it to them.