You are wise to be suspicious if they won't give you the name of the person calling; there are a lot of Nigerian scams going on with the IP relay call.
Scammers Using Internet Phone Service For The Deaf - O'Reilly Digital Media Blog
If you have listed puppies for sale, there are many scams other than this. Another one is where they send you a money order worth more than the dog, and ask you to pay the half back. The money order is worthless, but your bank may take several months to find this out.