Private credit card/debit card exchanges?
If you operate below the radar that practice can thrive.  For instance, if you were to accept a friend's credit card swipe using your Square dongle for the sale of your bitcoins, you'ld probably be in violation of the merchant agreement.  

If the charges are from friends and family and only made occasionally Square will probably never know nor care what the reason was for the purchases.  But start doing regular "card not present" tranasactions for larger transaction amounts (e.g., $100 or more) and that's probably when you'll end up getting asked for more details on your business activity.

Do know that you expose yourself to the risk of a chargeback should a payment dispute occur.