Sorry for writing in English, my German writing is not that good.
Don't do it. This way of paying is spread amongst people trying to set people up.
I too had two similar mails after putting a drum up in quoka.de and ebay kleinanzeigen.
After googling this kind of payment, its clear that they just want to get your money.
When I said I only wanted to deal through a normal bank transfer, I didn't hear from them again.