Today I went with a friend to an upmarket grocery store, Thrupps. He has an account there, and so did the lady in the line behind us. To use the account you fill out your 4 digit account number on a piece of paper and scribble your signature. About 5 minutes in the store will get you at least one account number. I got two in less than that. I don't know if this counts as authentication but rather arbitrary identification. A simple token would make a big difference. I would be interested to see how much they loose this way as there are other factors to take into account.

1. There is a security guard to the center keeping the 'rif-raf' out.
2. The patrons are mostly upper-class and might not pay as much attention to their bills.
3. In some cases the patrons are known by face, but this does not seem to be the norm.