As if people weren't already intimidated enough by wine generally and ordering wine in restaurants, their wine is usually served in what appears to be a needlessly complex ritual that almost seems designed to make a person either feel like an ignorant outsider or a snobbish insider. Yes, there is a bit of ritual involved with serving wine but each part of this wine ritual serves a purpose — generally to help ensure that you get the right wine and enjoy your wine experience. Learn to enjoy the wine ritual along with your wine.
Wine Bottle Presentation
First, of course, your waiter or sommelier will present the wine bottle to you or to whomever actually ordered the wine. The purpose here is so the person who ordered the wine can inspect the wine bottle to ensure that the wine they are receiving is, in fact, the wine they ordered. This isn't an idle concern because small but significant percentage of wines presented are not the right ones. You took time to decide on what wine you want and you're paying a lot for the wine, so you should actually get the wine you ordered, shouldn't you?
This may be less likely to happen when you're dealing with a professional sommelier, but it's still a real possibility so if the wine is being presented to you, take the time to check the varietal, winery, and vintage. There are also other aspects of the wine which you should inspect, like if it is the right temperature. Although it shouldn't be an issue, ensure that the cork and foil are intact — if not, it's always possible that the bottle was refilled with inferior wine. If you have any doubts, you should ask to be sure and even send it back if anything doesn't seem correct.
Since the cork and foil are supposed to still be intact when you receive the wine, the next step is for the waiter or sommelier to remove the cork and then present that to you. Although this may seem unnecessary, it allows you to ensure first that the cork is in good condition (no mold, not broken up) and second that it smells fine. If the wine is in especially bad shape, the cork itself will carry a strong odor and warn you not to drink it. If the cork is moldy or, alternatively, dry and crumbly, then the wine may have spoiled and also shouldn't be drunk.
Fortunately, all of these possibilities are very rare. If you order and drink wine regularly in restaurants, you might have a problem once in your entire life. Should there ever be a case where your are concerned, then just smell and sip the wine very carefully during the next stage of the wine presentation. You should know very quickly if the wine is acceptable or if something has happened to it. Don't accept any wine you think has spoiled.
Wine Decanting & Presentation
Once you've approved the bottle and cork, it's time to actually approve the wine itself. If the wine needs to be decanted, your waiter or sommelier will do so then they will pour a small amount of wine into your glass. No, they aren't being stingy with the wine — they are waiting for you to smell it and take a sip. If the wine tastes fine, then say so and a full measure will be poured for everyone at the table. If there is anything wrong with the wine, though, say so right away — this is the time to send it back, not after everyone has had their fill.
If you are unsure if the wine tastes OK or not, ask someone else at the table to check it for you. It's better to admit your ignorance now than for someone else to notice that the wine is bad a little bit later — or for you to notice later, after everyone has drunk some. It's not an ideal situation either way, but honest ignorance is preferable to getting sick on spoiled wine, especially if you are entertaining important people.