Is this question for real? - The point of TASTING wine in a restaurant is to see whether or not you'll enjoy it enough to buy a glass or a bottle. Just becasue you taste it, or have a glass, does not mean you have to buy the bottle!

the purpose of tasting the wine prior to pouring is to check that the wine has not turned sour. One may refuse the bottle on those grounds, but once the wine has been poured, it is considered sold. A possible out is if everyone at the table agreed that the wine was bad, but only after a sip. After pouring it is difficult to prove that the wine was unused at all.

Yes. If they opened the bottle at your request, offered you a taste, and the wine is good, you have to buy the bottle. The reason you're offered a taste is on the off-chance the wine has gone bad -- that doesn't mean it's bad in that you don't like it, it means it's 'corked' or 'cooked' or otherwise spoilt. If it has gone bad, no, you don't have to pay for it, but that's not very common. And probably the manager will have to agree with you that it is bad. Many restaurants offer a selection of wines by the glass or half-litre. If you order these, you don't pay for the bottle, just the portion you ordered. Again, at first sip, if you realize the wine is bad, you shouldn't have to pay for it; but if you simply don't like it, you'll likely have to pay. And this would be the one instance when you can ask for a 'taste' before ordering the wine itself. But if they only serve the bottle as a bottle (not by the glass etc), you can't ask for a taste without ordering it (and thus having to pay for it). That said, restaurant conventions change from place to place. If you ever aren't sure, you should ask ahead of time or at the time.

You shouldn't taste it anyway. Its way overprice.

Most five-star restaurants have most of their wines, available or are willing to bring you a glass of your chosen selection to try, if you have never tasted it before. Their hope is that you will enjoy it enough to BUY A BOTTLE. If you request a specific bottle that they open at your table, and IF if were to prove to have gone bad, somehow, the Wine Stewart would also try it then, and if proven to be off...you would not be charged. If they are truly a top shelf establishment, they might even comp you a bottle of something else, or offer you a free dessert, or an after dinner drink of your choice...because of the inconvenient experience of having offered you something inferior! However, there is also some respectability and "honor system" expected on YOUR part too. One does not show up at a fine dining restaurant with the expatiation of having a "Wine Tasting" experience before dinner. While such an establishment MIGHT well HOST an actual Wine Tasting event...that would be a specific event that is conducted to high-light the offerings, most often by a local winery to promote their products, and then you would be permitted and encouraged to sample an assortment of wines, so as to better understand their offerings, and usually purchase those you find most enjoyable.

If you order a bottle of wine and the waiter pours a drop out for you to taste, and after sampling it you do not like it, you are not obliged to purchase it. The restaurant is quite used to people sending the wine back for another to satisfy their customers taste.

No, but you MAY be charged a "Corking fee" for each bottle you have opened.