how not to be fooled when selling mobile phones

i was selling my mobile phone on ebay and the bidding went up and up and i couldn't believe the price it was, i awaited payment as we all do, then i received an email stating that my payment has been received and would be sent to my pay pal account when i sent the parcel internationally signed for tracking number to them, they would instantly send my money to my paypal account, unfortunately i was pretty new to ebay and pay pal and i