This has been in the news lately that waiting staff are frequently being made to pay the bill if customers walk out without paying.
When I was waitressing, one place did not have this policy but the second place I worked did. Thankfully, I never had any walk outs but other colleagues did and had to pay. Problem is, it really wasn't their fault.
We had around 20 tables to look after, multiple entrances which couldn't been seen from all points of the restaurant plus the usual going in/out of the kitchen, getting drinks from behind the bar. This made it massively difficult.
Personally, and maybe I am being unreasonable, I think it's appalling making waiting staff who are not well paid as it is pay for dishonest customers who up and leave without paying. Restaurants should have insurance to cover this sort of thing surely?