Sounds like Marco made a mistake. Maybe bring up this particular error to him and perhaps he will give you a refund this time if you mention they are supposed to be hot-stamped with a design on them, because in the end this helps him as well so he can correct the issue on his storefront. He is probably assuming himself that the targets are blank from the factory, hence his confusion when dealing with your request and why he would think it is crazy, since likely as far as he knows "they are correct".
He probably looked on IPDB and saw the blank ones and assumed that was it, unless those are a Marco set themselves.
What exactly did you say to him? Did you just tell him they were "WRONG!!!!!" or did you explain how this game originally came with stamped targets and that his inventory had an error? If you weren't clear about it, he is probably assuming it was your fault and you ordered the wrong thing and now you want a refund. Kindly enlighten him with details about this legitimate error on his part and perhaps he will have a change of heart.
If you weren't explaining to him the exact issue or if you were rude and blunt about it you are both at fault.