Unfortunately there is no high success rate of getting such reversals fixed. Yes, you are correct in that it is possible to win a dispute with digital goods, but not with a high success rate. You'll lose way more than you'll win because in the end, proving the validity of the transactions in question is near impossible.
Paypal wants to see that:
A. The buyer's payment with legitimate (not a hacked Paypal or stolen credit card)
and
B. The buyer received his/her goods in the condition described
Even if you were to come up with a solution for "B" (which is no small feat in itself - even if you somehow could confirm delivery, then you also have to worry about the second part - the condition. They can easily say that yes the received the item, but it wasn't what they ordered. For example if you sold a $100 digital gift card they could say only $50 was on it when in reality they just spent half of it. At that point it becomes your word versus theirs and Paypal will always side with the buyer when it gets to that.), then "A" is a buyer's get out of jail free card.
In most cases you can't prove that a buyer's payment was unauthorized - that's really up to Paypal. You can have "A" covered if the buyer used the same computer with the same cookies, same IP address, same credit card as usual, etc, but if a buyer is smart enough to file a dispute, then chances are they were smart enough to do basic things to cover their tracks. There are indeed a few of these scammer buyers who are stupid enough to try and commit fraud and not cover their tracks, and well, that's when the rare success happens.
When you call Paypal you need to keep in mind that Paypal doesn't care. They barely allow digital goods in the first place. At least on the US website (of course, Paypal in different countries have different rules so this may not apply to you), digital goods are not included in their seller protection. From their User Agreement (section 11.5 - see here: https://www.paypal.com/us/webapps/mpp/ua/useragreement-full),
11.5 Items/transactions not eligible for PayPal Seller protection. The following are examples of items/transactions not eligible for PayPal Seller protection.
Claims or Chargebacks for Significantly Not as Described.
Items that you deliver in person, including in connection with In-Store Checkout.
Intangible items, including Digital Goods, and services.
PayPal Direct Payments.
Virtual Terminal Payments.
PayPal Business Payments.
All in all, I wish you the best of luck, but do not expect to win many of those disputes.