I agree that paying by cash can help move things along, but that's the only one (in my opinion) argument for this kind of payments. I don't want to say: 'don't take cash', just: 'give your customers a choice. give them a chance to pay at least by cash, or by card'.

As for an amount of purchase... I understand transaction fee problems related to these kind of things. That's why I think that people need to realize that if they want to pay by card - they need to buy something more then just a newspaper. Unfortunately we can't jump over the bank charges.

However... it would be a really good idea to build a system, which would take money from your bank account or a credit card once a month for all the things you bought in that month.