[wideawake]

I already know humans can't pay for the forgiveness of sins

Indulgences have nothing to do with the forgiveness of sins.

Again, you fundamentally do not understand what Luther and Tetzel were arguing about.

[xone]

The fraud sold forgiveness of future sins or to pay to have someone relieved of time in purgatory.

Since these are of no account, I don't really care what the Catholics say about indulgences/good/charitable works and their effects. The wares bought and sold during the time were for remittance of sin. Luther complained that if the money could remove someone from purgatory, why didn't the Church do it for free for everyone. Because debts needed paying, basilicas needed building and profit must be made off the rich and poor faithful in their ignorance.