I asked my sister to buy me some shoes from a store. Because she only has a credit card (and no debit card) I didn’t want her to pay and then have me pay her back because of ribis. So I said that I’ll buy them off of her instead (ie pay her more for the shoes than she paid). Is this mutar?
If you give her the money before the credit card is due it isn’t a problem of ribbis because the loan didn’t accrue any interest. I don’t understand why buying from her will help, because you are the one who bought it with her money, and it belongs to you, not to her. Therefore just make sure to give her the money for the shoes right away and then you are fine.