Thats paypal.
I'm still slightly confused to how you know the perfume is fake. How different does it smell to the original? Its not like clothes etc where you can see bad craftsmanship or poor quality materials. I'm not doubting you at all, just interested
Trading standards would be worth a call as well. I would even suggest that you will accept his £15 but the perfume is with trading standards and he is able to contact them to have it returned. He must know its fake if he has given in so easy having specified returns conditions.