What is the ruling on buying dollars with a card and then selling them to the shop owner for local currency?

Purchasing dollars with local currency is a type of currency exchange (sarf), which requires mutual possession (taqabud) at the same sitting. Delay is not permissible in it, nor is purchasing on credit. As for bank cards, some are covered (prepaid/debit), in which case possession is realized when purchasing with them. Others are uncovered (credit), in which case possession is not realized when purchasing with them. Accordingly, it is permissible to purchase currencies with a covered card, but it is not permissible to do so with an uncovered card. If the exchange is valid, and the questioner takes possession of the currency, there is no harm in reselling it.