I don't know the details, but the gist of it is that you will be offered a credit card for a purchase, and it will be approved by the card company, only to be rejected a few days later (presumably after you have already sent the goods). I can't remember all of them, but there's a list of countries that are the biggest places to watch out for. I believe it started as an ebay scam. I will try to get more information about it. I only know tidbits of info, because I had received some very suspicious sounding emails to my generic business email, and did a little digging. This was about six months ago...
I don't know if that is why this would happen, but it may just be the fact that someone is being wary about it...? Who knows!