The Escrow Mechanism
When you purchase an item on the drughub tor site, your money does not go to the vendor. It stays in the market's Escrow. Only release the funds ("Finalize Order") after you have received and inspected the goods.
Disputes
If the package does not arrive, do not Finalize. Open a Dispute. The drughub market moderators will review the case. You will need to provide proof (often impossible for digital goods) or rely on vendor reputation.