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Most restaurants are not legally required to accept returns just because you didn't like the taste, unless the dish is poorly prepared or contaminated. If the food has a real problem (undercooked, burnt, something foreign in it), then they should definitely swap it out or give you your money back!
It really depends on the restaurant, to be honest. I once ordered a dish that arrived cold and complained, and they had no problem swapping it for another one; but at another place they told me that if I didn't like the flavor they couldn't do anything about it because I'd already tasted it. The important thing is that if there's something **actually wrong** - burnt, raw when it should be cooked, or something weird - they do have to make it right, but if you just didn't like how it tasted, most places aren't obligated to take it back.
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