i couldnt understand that credit card deal

They are taking credit cards that are returned (but sent out pre-authorized) and using them to buy goods, which then they fence. Hence the goods bought on the credit cards cost them nothing, and when they sell those goods it is pure profit for them.

he would get money because he would use dead people's credit cards to buy things and then resale them for a cheaper price. It is basically saying he is getting free stuff and then selling it to make money!