Hi Andre Silver Badger ,
For the specific question, I can only agree with the answer from Dominik: A transfer is normally not retrievable once it has been executed.
Concerning. your situation: inquiries at electronics sales on eBay Classifieds from abroad are actually always fraud. I would sell such devices only within Germany, everything else is too risky. If you wait a few hours / days, you will probably also receive an email from eBay stating that the buyer's account has been blocked for fraud.