You can use the Classifieds & Listings apps on the same website, but they would require separate pages in the setup/display - for example separate post forms, search forms, classified page, listing page, classifieds directory, listings directory, etc. You can create different categories for the Classifieds and Listings apps.
The Listings app also includes features for posters to sell items. Please refer to the Features page at https://www.ultimatewb.com/features for more info.
Please feel free to ask if you have any further questions!