Classified Ad App for Android

The application about buy and sell just like a classified ad where members can post their items for sell. No product inventory is needed. *Specifications* Users will be able to Post product with name, image, title, description and contact button. View products through by browsing categories. Each product/post will be either offer or wanted. Contact button allows the buyer to contact the seller. Message is sent to the email. No PM feature. There has to be add, delete and edit a post. Note: post and product are used synonymously. If there is a way a seller can edit or remove his/her posts without registration, then there is no need to program the login/registration. Owner of the app can remove and edit any post as needed. I believe these are the most necessary basics that is needed for a classified ad app to run. If i forgot something important, you can go ahead and add it, just let me know before adding a specification. Hence, just not to go wild, i can discard the feature of report/spam and captcha. Not needed...Are they important for smartphone app?