When you buy on amazon, amazon charges your card not him. To accept credit cards directly requires a fair bit of setup including a merchant account and all that. Doubt he has all that setup for what is most likely a side thing.
I get it....PayPal and CC companies are NOT friendly at all towards the BTC community. Sometimes I feel that one thing keeping BTC down is the ability to quickly transfer USD to BTC without paying 10-20% premiums. I also understand that usually there is a fee to the merchant, but some of the places out there converting BTC to USD either don't have the technology to keep up with the volatility or are just plain gouging people.