Comment by derefr

I think they're talking about when merchants insist that you give them cash ("cash only"), not when buyers insist on giving cash. The usual assumption is that if e.g. a street-food cart is cash-only, it's not because they can't accept cards (it's rather trivial nowadays) but rather that 1. they don't want to pay the interchange fees, and more importantly, 2. they want to be able to cook their books when reporting revenue.