Sorry, if your buyer paid through Paypal, then without DC the buyer wins EVERY TIME. No exceptions. Always print labels thru PP, it's so easy and DC is free with Priority mail. 18c with First Class mail (pkgs 13 oz & under).
If the buyer files a dispute/claim PP will depend on that DC number. No DC? Refund for buyer. Unfortunately there are dishonest people out there who will file a claim to get their money back if they see no DC on their package.