This has tripped me up in stores. You bring 1 item and they tell you, "This thing is two for X (price)". If you then say "Ok" disinterestedly, will they sell you one or two of those?
You left out the rest of the sentence which makes it an incomplete sentence. Usually this is followed by "would you like another?" or something along the lines that becomes a yes or no question.
Merely saying "This is two for x." is a statement, not a question.
That's why I make it a point to say "I see", "uh-huh" instead of "OK" to such statements, given that it's so easy to be misunderstood even though technically "OK" is an acceptable response.
