SATTV: Just bring out the zip zap machines and do manual transactions, a bit of a pain but at least you get the sale.
Most people dont realise that you can do a zip zap for eftpos but you can.

Although what happens if someone uses a cancelled eftpos  card or overdrawn, which would have failed if done electronically . Also people could use a card they have found, as some eftpos card don't have a signature field on the back. Who wears the loss, the bank or the retailer?

If it's overdrawn, the bank forces the transaction and simply overdraws the account. If it's a cancelled card, depends on the reason. It's possible for a cancelled card to still accept charges under certain circumstances. If you cancel a credit card for example, as long as it wasn't for a lost or stolen card most banks will still process charges from insurance companies, voucher transactions, and hotels.