What are the laws for shipping firearms?

I bought an old iver johnson single barrel champion a while back in michigan. the guy promised me that he could mail it to my house in maryland, in which you can legallly own a shotgun without a firearms permit of anykind. may I also say it was'nt in firing condition but i could easily have fixed it with the purchase of a few parts. anyways after getting my hopes up for a week he calls and tells me that "I thought you were talking about a toy gun, no I can't send this to a person across state lines to someone without a firearms permit" Now I know i don't need one to have it here but he sent my money back before i could tell him. So is what he said true? Is it illegal to send a firearm "that doesn't work" across statelines to someone without a firearms permit if one is not needed in that area?