Yes, especially if

1. You have a doubt about the authenticity of a product that is for sale.
2. To complete the product information.
3. To correct erroneous information
4. To show that you value this product
5. For an interesting and constructive comment

No for

1. To say that the price is too expensive ... the seller is free to choose his selling price
2. To insult and say unpleasant things that have nothing to do with the sale of this product