Third party sellers (on Amazon and other retail sites) are affiliated with wholesalers carrying your book. Since these sellers are partnered with the wholesaler, they have access to your book, and can list it on a site for whatever cost and condition they want. Normally, the third party sellers do not have any books in their possession, and often will order from their wholesaler after someone purchases from them.
Your royalties will not be negatively impacted by these retailers.
