No, it isn't safe. It's important that the buyer pays by PayPal through eBay's checkout. If there's a genuine problem in paying they need to sort this out with Paypal themselves.
There is a regular scam by which the buyer persuades the seller to disclose their PayPal details, then sends a the seller a convincing fake email, pretending to come from Paypal, stating that payment has been made and the seller should now post the item. There was no payment, of course.
