I think what is being asked is he wants you to sell him just the parts needed to be used to build a slot car. And for a price less than what you are asking. I'd just say you are not interested in selling a partial kit.
I don't answer unknown calls. If its legit they will leave a message. I usully check on line to see if others received the call. I then block the number on my cell. Cuts way down on nusience calls.