A concierge can obtain a table or a ticket that a guest calling directly cannot. The advantage comes from a relationship with the venue that has been built and maintained over years.
Restaurants hold back capacity
Sought-after restaurants rarely release every seat to public booking. A portion is retained for regulars, for walk-ins and for relationships the restaurant values.
Hotel concierges are among those relationships, because they deliver a steady flow of guests who spend well and cause few problems.
When a concierge calls, the request is handled against that held capacity rather than against the public availability a guest sees online.
The relationship is reciprocal and monitored
A restaurant extends access on the expectation that the concierge screens requests, confirms attendance and takes responsibility for no-shows.
A concierge who books tables that go unused loses the access, so requests are filtered before they are passed on.
This is why a concierge confirms details carefully and follows up before the reservation. The obligation runs in both directions.
Professional networks extend the reach
Concierges belong to professional associations with members in most major cities, and a request in an unfamiliar city is routed through a colleague there.
That colleague holds the local relationships, so the guest benefits from a network rather than from the individual at their own hotel.
The same network handles unusual requests, since somebody in it has solved a version of the problem before.
What is realistic and what is not
Lead time is the largest determinant. A request made when booking the room is far more likely to succeed than one made on arrival.
Genuinely constrained supply cannot be conjured. A restaurant with a small dining room and a long waiting list will decline most requests regardless of relationship.
Being honest about flexibility on date, time and party size converts many refusals into offers, because those are the variables a venue can move.
Tipping and using the service well
The service is included in the room rate, and asking costs nothing. Tipping is customary for a request that took real effort, and is judged on effort rather than on the bill.
Specific requests outperform vague ones, since a concierge matching a stated preference does better than one guessing from a category.
Cancelling through the concierge rather than silently abandoning a reservation preserves the relationship the whole system depends on.