Not quite the level of the infamous Wendy's finger-in-chili scam, resulting in nine year prison sentences (possibly reduced through appeal) for the fraudsters.  Of course, they were looking for a bigger payout than free food.

Angling for free food on a smaller, less bizarre scale, scammers target restaurants with the object (glass or bug) in food gambit; complaining about quality after consuming the entire meal; making the food poisoning phone call; and the Dine and Dash, easily converted to the Smoke and Dash in cities with an indoor smoking ban.

Here's a representation of Dine and Dash methods from the British television series "The Real Hustle."

Some restaurants dock wait staff for customers who leave without paying the bill.  Not to mention the practice creates higher prices for everybody and suspicion for legitimate complaints.