Twist a page with your fingers. If it is thicker and feels a little numb, it is generally better paper.
Second, it depends on whether the printed words are uniform in color, because in a genuine book, all pages are the same in color. Piracy will have some pages with deep words and some pages with light words.
Third, look at the cover, whether the color is even and bright, and it looks more comfortable. Because the color of genuine books is a thousand choices, the color of pirated books is generally poor and looks ugly.
Because pirated books are generally reproduced from genuine books, the contents are almost the same, but there are differences in printing and packaging. Good luck and good luck!