This is a yes and no answer. As an eCommerce store you will have probably taken your product descriptions from your supplier, so you will find that everyone else who also purchases from that supplier use the same description. In that respect Google expects that people will have similar or the same product descriptions and your rankings wont be hurt by that. HOWEVER SEO isn’t just about ranking and owning an eCommerce store isn’t just about getting visitors, it’s about sales. Google want to provide the best results to the people searching, so if you can write a better description, provide all the benefits or the products you sell and answer any questions they have, you will have a better chance of converting that visitor to a customer and also Google will reward you with better rankings because your content is different and provides all the information a user needs. Having better conversion rates due to better descriptions also means fewer people will bounce back to Google and click another supplier so Google will know that your site is useful again giving better rankings.