A physicist’s financial experiment netted him $300,000 From Credit-Card Rewards https://www.thestreet.com/mishtalk/economics/man-makes-300000-racking-up-6-4-million-in-credit-card-charges
°American Express card offered unlimited 5% rewards at grocery stores and pharmacies after he had spent $6,500.
°Use reward cards to buy $1 coins from the US Mint. The transaction has no shipping charges.
°Used gift cards to buy money orders, then used the money orders to make deposits in his bank account, then used that money to pay his credit-card bill.
°In a $500 transaction, the 5% rewards would yield $25—more than enough to cover gift-card fees of about $5 and the $1 fee on the money order.
I don't really understand all of the scheme, but it seems legit.