as other's have already said; it's vitally important to make sure you have seller protection through paypal and meet the qualification criteria for each specific transaction. keep records. if you don't, there is no way to guard against a chargeback because in most cases, the bank will find in their customer's favour despite you providing proof. 

i've had a number of chargebacks of which i've done everything right; taken all the necessary steps to meet seller protection and the only reason i ended up getting my money back for the transaction was due to it being covered by seller protection. otherwise, i simply would have lost out. 

the first thing to ensure is that you have proof of tracking. if you don't, you pretty much don't stand much of a chance - no matter how low-value the item is or whether or not you think it's fair. it's one of their conditions and if you don't factor in the fact that 1 in x amount of transactions will be lost/claimed as not delivered/chargeback then you're going to end up sending yourself crazy.

even though as digi said intangible products are covered, be sure to make sure you know what category they fall under, whether they are covered and if you're unsure, enquire with paypal before listing / selling. i'd say if it's a digital download for a game code it would fall under the downloadable / digital content. though, others may know better than me in regards to that. i think it's always pretty hard to prove that the code hasn't been used prior to selling or that it even works (which is why i think it's in the category if items not covered by protection).