Basically, it was an elaborate scam:
I had emailed someone from PetLoop.com for a Yorkie. He replied that he had no more, but someone who he had sold to had to re-sell, since they were being relocated to Nigeria. I e-mailed this other person and we spoke over about 25 e-mails, and I was pretty convinced. We agreed that I'd send $200 up front, and the other $150 upon receipt of the dog.
After sending the payment, I didn't hear back again, but I did see that the payment was picked up (Western Union).
So we lost our $200. Luckily I was smart enough not to give her the whole sum up front...
I now see that these scams are pretty common - since then, I've gotten at least 4 other similar emails. But the bottom line is that we still have no Yorkie