They'll get robbed more often and this will be brought to their attention. I think the reason they didn't do a ban is because they know that. I keep picturing a situation where someone is robbing the customers in there and I hand them this wallet.
https://farm6.staticflickr.com/5568/...6f9280_c_d.jpg
And of course there is some witty dialogue and I point out that the customers haven't actually been disarmed.
https://farm4.staticflickr.com/3890/...933db1_c_d.jpg
Of course for that to happen I'd have to eat there, which I only do when my dad is visiting it seems.