PayPal is one of the riskiest payment methods and a favorite of scammers. Ask for ID with selfies and signatures and check for photoshop. http://fotoforensics.com/ It is best to call PayPal and tell them you are selling bitcoin as they allow it.
The Seller of bitcoin has a time limit of 30 minutes to pay for the bitcoin before the trade is cancelled by the system. Trade won't auto-cancel when buyer has marked trade as paid. After that buyer has to wait for seller to release bitcoins.