> How does anyone (issuing bank, acquiring bank, Upwork, or contractor) figure out whether "the client was authorized by the cardholder to use the card"?
This is a reasonable question, but the answer is quite simple: The bank asks. You'd be surprised how readily cardholders admit to giving their card to someone.
If the cardholder claims charges are unauthorized, that claim is investigated as fraud, not as a billing dispute. In either case, for the amount of these charges, the bank would do more than a minimal investigation. Lying to pursue a chargeback for your own charges is just as fraudulent as someone else making unauthorized charges.
This is a reasonable question, but the answer is quite simple: The bank asks. You'd be surprised how readily cardholders admit to giving their card to someone.
If the cardholder claims charges are unauthorized, that claim is investigated as fraud, not as a billing dispute. In either case, for the amount of these charges, the bank would do more than a minimal investigation. Lying to pursue a chargeback for your own charges is just as fraudulent as someone else making unauthorized charges.