My wife and I always order a bottle of good wine when we go to a nice restaurant for dinner -- that is, unless we can bring our own, which is fairly common in California (most restaurants charge a corkage fee -- we try to avoid places that hit us up for more than $10). Decent wine is usually at least $20 or more per bottle (sometimes way more), and I expect to get my money's worth.
Fortunately, most of the wine I get in restaurants is fine, but there are occasional exceptions, maybe 1 in 20 bottles or fewer. Some bottles are "corked" (a smell and taste like wet cardboard, which comes from a cork that's infected with some sort of mold), or it tastes like prunes from having been exposed to excess heat, and sometimes it's oxidized or tastes like vinegar or sulphur. These wines I send back after smelling and tasting them and consulting with the owner or server. They usually agree with my assessment and are apologetic, but sometimes they obviously think I'm pulling a fast one. Too bad for them -- it's my money! And there have been plenty of times that I've decided halfway through the bottle that it's bad, and I live with my mistake.
I've never sent back a good wine (i.e., one without noticeable flaws) just because I didn't care for it. However, I've seen many people do that, and it ticks me off because it forces the restaurant to keep its prices high, and it might make the owner all the more suspicious if I ever object that a bottle's bad.
The worst example of this that I've witnessed occurred several years ago at a very nice Northern Italian restaurant in L.A. one New Year's Eve. Seated next to us was a young man and his date, both barely 21, dressed to the nines. I noticed when the young man sent back the wine he had ordered, complaining loudly to the waiter that it wasn't "good." The waiter rolled his eyes and dutifully brought another bottle, albeit an entirely different wine. I watched as the young man took a taste and promptly rejected this second bottle, too, basking in the adoring gaze of his duly impressed date. The waiter then brought a third bottle, also a different wine from the first two, and having strutted his stuff for his girlfriend, the young man accepted it. I managed to ask the waiter if there was anything wrong with the two bottles, and he said they were fine -- and that the kitchen staff was enjoying them immensely. It's a good thing for the young man that this was a classy joint -- if it had been my place...