If this is totally out of the blue and not someone you know and trust, then I would be extremely wary.
I have heard of people doing stuff like this and then issuing a chargeback on their card after the fact (to get something like a free stuffing video, etc). If that happens after you've already spent the money, that could leave you in the red.
As the saying goes, "if it seems too good to be true, it probably is".
2 weeks