Unfortunately the combination of Craig's List and PayPal is never the best recipe for a happy ending. Scammers read and understand the User Agreement and know what they can get away with. Tickets are not covered for buyer or seller protection as they are considered under services. Additionally you said you emailed the tickets, not good either as you have no shipping or tracking information not to mention the tickets would be also be considered an intangible item.
One could go dig a little deeper here and ask how you sell the items, meaning, did you send an invoice to the buyer? Or did the buyer simply use the Send Money Feature. There's really so many things here that can contribute to a risky transaction. This is where scammers get the upper hand and honest sellers get nothing.
Most likey, the scammer got the tickets. He or she knows that they can claim they were never sent or received because they know you won't having any acceptable shipping or tracking information to prove otherwise. PayPal looks at the claim, want to see your receipts for shipping and wants the tracking number. You don't have it, PayPal then refunds the money and the rest is history. Sad to say, you can't fix it.
Here's a few tips for protecting yourself:
What works best with PayPal, only sell physical items that can be shipped, insured and tracked. Sending invoices to buyers or having a web page setup for purchasing. (Don't allow the buyer to use the Send Money feature to pay.) Require a "confirmed" address meaning that the buyer must have the same shipping and billing address. Don't ship international, you run into tracking issues and it also wastes time. Note, you only have 45 days to file a claim, shipping international uses up most of that time which can hurt you. Use the Fraud Filters if they are available (not everyone has them yet). Don't accept eChecks and sell only to US PayPal Accounts.
