Are these sentences natural to a native ear?
1. Without going into too much detail
s, how did you achieve this?
"Detail", not "details".
2. Thousands of people gathered in the square and protested for (a) change (is the article before 'change' required?)
No article is required but you don't really protest for change. You usually protest against something. They may have "called for change". I would say something like "They demonstrated in the square, calling for change".
3. The good thing is that they are able to find product even in these tough markets. ( should there be an article before ‘product’)
Yes, although without context it's impossible to say whether it should be definite or indefinite, or whether the singular or plural is appropriate.
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