Thus, if an author has in general a positive opinion of a product, the probability of a negative sentence appearing in a review is lower than that of a positive sentence, and even if a negative sentence is introduced, it is likely to appear together with a concession or a contrast marker, such as although or but, or be modified by a hedging expression, such as might, only, could be, which mitigate the negative effect on the reader.
the author makes us understand that his primary opinion of the product is still positive, and uses the discourse relation of contrast to present an opposite opinion.