How many reviews should I trust before buying a shampoo?

High review volume with a steady 4.5-plus average (as with Olaplex N°4 at tens of thousands of ratings) is a stronger signal than a near-perfect 4.8 average on fewer than 100 reviews, which is easier to skew. Cross-check the rating distribution and look for repeated mentions of your specific concern, such as frizz, oiliness, or scalp sensitivity.