Here is a sample email:
Hello. I bought a puppy from a guy in Cameroon and he was shipping her to me this morning. Now he is saying that she is at the airport and that we have to pay $1200 for a pet den. Is my new pet even there? I already paid for her.
We hate to be the bearer of bad news. But, in all likelihood, you have fallen for a scam. We get notes like yours fairly often from people who have been the victim of pernicious deceit.
Whoever sold you this probably never had any intention of providing you with a new pet. So please do not send any more money down this very deep hole unless you want to enrich a scam artist.