Drinking and driving is a bad thing, no one denies that. Restaurants have to be aware of the danger of over serving, but also have the advantage that they are plying their customers with food, as well as wine. This allows, for some customers, the opportunity to have a little more wine.
The primary tool in a restaurant for selling a second bottle of the same or different wine, is the pour. A well trained staff will never allow a wine glass to be empty. Ideally, the party should have finished the first bottle just as their appetizers are being cleared. For larger groups it should be considered an absolute that you can sell them another bottle at this point, but even small parties will be out of wine when their main course comes.
First rule of sales - never ask a question that can be answered yes or no.
Don't ask if they want another bottle, this leaves it open to a snap "no" and your hopes are instantly shot down. Better to interact with the customer by saying something like "Well, I see you enjoyed that, would you like the same or something else?" A wine list should be at hand.
The more advanced technique is to say "Since you seem to have enjoyed that bottle, you may enjoy [slightly more expensive wine]. Would you like to try it, or another bottle of the same?"
The most advanced technique, and the one I personally employed to sell an astounding amount of wine, is to lead your customers through a flight of wines from the outset. This is easiest with repeat customers that you already have a rapport with, but it is also the way to ensure repeat customers. An aggressive wine by the glass program can really help.
As you hand them the wine list you ask "would you like to pick the wines this evening, or would you enjoy having me put together an experience for you?" If they bite, you start with a bottle (or half, depending on the size of the party) of sparkling. Move on to white and or red, but above all else, finish with dessert wine. This is one of the reasons the half bottle is a valuable weapon in a restaurant's arsenal.
These common sense, but practical bits of advice are great for on premise accounts, but what about retail outlets? A lot of the same techniques can be used when someone comes in asking for a wine to pair with dinner, but the real holy grail of retail is the case sale.
Case discounts may drive some to buy a case, but it is only half a tool. A good salesperson will keep track of their customers and their purchases, so that among other things they can use the 11 bottle case technique. Simply, you recommend a bottle and let your client know that if they like it, you will still offer them the case discount on the other 11 bottles, should they come back in for them.
This is the basic approach, once again I have an advanced sales technique that your staff should be using. Evolution. When the client is thinking about a wine that could potentially improve with time, the salesperson enthusiastically recalls how much fun it is to buy a case, to drink a bottle now and then over the years so "they can see how it evolves."
The most advanced case sales technique requires careful buying. One of the most valuable tools in any type of sales, is scarcity. Buying small run wines, or hard to get wines, allows you to offer them to your better customers with the admonition that "this wine is so scarce, if you love it and want more, we will probably be out of it. Your best bet is to buy a case of it now, to be safe. And speaking of safety, I will be happy to take back the other 11 if you decide that it is not to your taste."
It is easy to see that the trick to selling more of anything, but especially wine, is to have a multi level plan of attack. Be prepared to offer your customers exactly what they want, before they know they want it. Staff, on or off premise, too often are order takers. This allows your customers to be in charge, and they are not nearly as interested as you are in you making a profit. Don't take orders. Sell.