There are many reasons why you want to allow your customers to leave reviews based on their interaction with you, both in-store, as well as on your website.
First of all, let’s distinguish between merchant reviews and product reviews. Product reviews (if you sell products online) is a service you can subscribe to and integrate into your website product catalog. This allows customers who purchase from you to leave a review of the individual item they purchased along with their buying experience. This is extremely helpful for new customers in that they can read real users personal (and often helpful) opinion of the item they are considering. The aggregate of customer opinions provide great user-generated information during the buying process and establishes your site as an authority on the items you sell.