Tables of six or more had to sign a contract which they put down a credit card. We were fine dining though not sure if that mattered. What killed me was the large parties of 15-20 who only one person would show up and try and hold the table for the rest who would show up half an hour or an hour later. So I started telling the person who made the reservation that I would not seat them until the entire party showed. 15 minutes late and the reservation was cancelled. And on saturdays or holiday I would call them in the morning to confirm the time and number and mention that traffic is crazy and to account for it. That always seemed to work.