To slow down the spoilage of open wine which is used for wine-by-the-glass offerings, restaurants may vacuum any air out of a bottle with either a hand pump or an industrial vacuum pump.
Alternatively, they may replace the oxygen-laden air in the bottle with carbon dioxide, argon, or nitrogen sprayed in the bottle and then tightly cap the bottle. There are also commercial wine preservation systems that use other inert gasses to replace air. These systems may prevent spoilage of the wine for up to 4-7 days depending upon how thoroughly they replace the air in the bottle.
Wine by-the-glass poured from a bottle that has been opened for 2 or more days should probably not be sold to guests even if the wine was kept refrigerated overnight. Wines with inert gasses or vacuum sealed will need to be checked daily by someone to ensure servability.