It is a common practice for eBay sellers to include information about their shipping, payment/billing, return policies, etc. within their listing descriptions. Since eBay is its own beast, so to speak, there is little negative impact on eBay itself, other than when a merchant has more information in the description about their shipping and policies than the actual product they are selling (this is all too common on eBay)!
However, if you are a ProStores merchant pulling in your listings from eBay to create your online catalog, this extraneous information (shipping, payment/billing, return policies, etc. — henceforth referred to as chafu) will negatively impact the Search Engine Optimization value of your content.
To distinguish your items from the thousands of others on the web, you need the best product descriptions possible. The content should be unique, original, well written (readable), pertinent, accurate and keyword-rich (not keyword SPAMed).
Product descriptions matter. The role of product copy is to give buyers enough information, so they could convince themselves this is the right product for them. Clarity trumps persuasion. The best sales copy is full, complete information. No hype needed.
Google actively looks for duplicate content in an attempt to show relevant and unique content in their results. If they see the same content pop-up on a new site they tend to lower the new site’s relevance in search (first come, first serve).
They are looking for content people are interested in finding on a page, so consider the content on each page carefully. Many good pages on a site will help the site overall by providing many contact points to your product pages.
In the context of the chafu noted above, Google's advice is to "Minimize similar content: If you have many pages that are similar, consider expanding each page or consolidating the pages into one..."
This is why a free-standing eCommerce site like ProStores has an About Us, Policies, and Customer Service pages, so pertinent information can be presented to visitors in a single location, not scattered across all of your product descriptions watering-down their SEO value.