There is a difference between a “sales refund” and a “sales reversal”.
A “sales refund” is processed and granted by Envato itself, and requires the buyer to contact Envato. After outlining why the buyer should receive a refund (based on the buyers explanation/justification), Envato might grant that refund, or not. In most cases, Envato will contact the author and get his/her opinion on whether a refund is justified, or not. Therefore, any “sale refunds” are fully under Envato’s control and are usually only granted if the item hasn’t been downloaded yet, or serious problems arose when using the item. Envato also only grants “sales refunds” for a short period after purchase. “Sales refunds” also only happen to legit buyers with a fully approved and processed payment.
A “sales reversal” happens from outside Envato, and occurs when the buyer goes through the payment platform s/he used for the purchase (i.e. Paypal). All it takes is for the buyer to claim to the payment processor, that the purchase is fraudulent, which will cause the payment platform to automatically request the money back from Envato. And naturally, if Envato has to give back the money it received, it will also take back the money you received from the purchase.
Most payment platforms give generous time frames during which a buyer can claim a charge as fraudulent, which is the main reason why a “sales reversal” can happen up to three months after the actual purchase occurred. There is absolutely nothing Envato can do about “sale reversals”, as those happen outside of Envato’s control.
Often times, many buyers who “feel the need” to claim a purchase as fraudulent, usually either did not attempt an official sales refund first, or had their request for a sales refund denied by Envato.
That is not to say that there is the occasional case, where a 3rd parties credit card information were stolen and used by others to purchase items, which makes a “sales reversal” legally required by the payment processor. And because most payment platforms don’t want to go through the lengthy (and sometimes impossible) process of having to prove to the buyer that the charge is legit, they simply opt to take the buyers word, and grant the “sales reversal” automatically.
In the end, bad buyers like this are unfortunately part of doing business (believe me, I had my fair share of those myself), and there is really nothing that Envato can do to prevent “sales reversals”. Only after one such “sales reversal” happened, can Envato disable and block the user account for further usage, which they usually do immediately.