SOME RESTAURANTS ALLOW CUSTOMERS TO BRING THEIR OWN BOTTLES OF WINE (AND SOMETIMES BEER OR LIQUOR) TO CONSUME WITH THEIR MEAL. MANY ESTABLISHMENTS THAT ALLOW BYOB (“BRING YOUR OWN BOTTLE”) CHARGE CUSTOMERS A CORKAGE FEE TO COVER THE COST OF SERVING THE WINE AND TO RECOUP REVENUE LOST BY THE DINERS NOT PURCHASING WINE FROM THE RESTAURANT.

Part of the reason why restaurants charge a corkage fee is to cover the cost and time associated with serving a bottle of wine. 
While the most basic service that restaurants provide is removing the cork from the bottle, you also supply customers with stemware (anything from a basic wine glass to a glass appropriate for that specific type of wine), refill glasses, and (potentially) chill the wine. The complexity of services provided for BYOB customers depends on the restaurant’s sophistication and the cost of the corkage fee. 

Many restaurants charge between a $10 and $40 corkage fee per bottle of wine. However, some corkage fees can be upwards of $100. 
Usually, the more expensive a restaurant, the more expensive the corkage fee. High-end restaurants offer an exceptional level of service and wine-related amenities, which is why they can charge a higher corkage fee than your favorite neighborhood takeout spot.