While you were ringing in the new year last December 31, restaurants around town were ringing telephones to find out what happened to their reservations. Le Bagatelle had 81 no-shows and cancellations. The Rive Gauche had 50, the Golden Table 30, Le Pavillon a dozen. This was after they had refused many reservations once their bookings were filled. For a potentially full evening they had hired extra help, ordered special food, even booked live bands. Le Gaulois solved the problem by requiring deposits, and will do so again this year.
Restaurants have tried every tack to handle reservations equitably. They take telephone numbers and call to confirm; still ther are no-shows. They overbook, risking getting caught when everybody unexpectedly shows up. They tell dinners that they can have an early table but that it must be vacated by some specified time; diners are insulted.
Early diners linger, and late diners are angered by having to wait for tables they have reserved. Restaurants have empty tables waiting for reservations, and people become infuriated when they are told no tables are available.
Some restaurants would like rules of thumb that are accepted by diner and restaurant alike. One of them has suggested that restaurants hold reserved tables for 15 minutes at lunch, 20 minutes at dinner (30 minutes for good customers of the house), then be free to release the tables. It's a start.