Perhaps after just two events that might seem a little harsh, but I definitely understand the store's reasoning here. You've got a guy that is pretty much guaranteed to lose you money in the form of his regular auditioning of big ticket items (can't sell that returned item for full price anymore). Why would a store want to keep a customer like that?

Even if you pay with cash, they still check your ID when you return things and keep track of how much you return.