I think in general refunds would not work. You won't be able to ask for a refund before you purchase something, so that's it. Unless somehow the seller did not send the content yet, and you changed your mind and ask the 3rd party to return your money back (which means it's centralized or at least a multi-sig).
But it's confusing considering how their purchase works. Which means either the buyer ask a refund before the 24 hours period started (when?), or before or if the payment is not confirmed:
Our platform uses a third-party service to process payments.
Content is available to download after payment has been confirmed.
Payment confirmation policy is described here.
Purchased content can be downloaded within 24 hours after purchase.
Source: https://btcfile.link/terms
As for now, refunds are not allowed. The original idea was to allow refunds after the purchase, but before the file is actually downloaded.