Hi Antonio, in answer to your questions:
1) There is currently no built in tool which searches for duplicates, so this would ultimately be a manual process at this time in terms of moderating listings.
2) The custom fields function is related to the listings themselves, so you can essentially have whatever information you need to appear in the listing.
3) The responsive design changes will be available in
Vantage v1.1.4, for which the release is imminent. It has already been undergoing beta testing so has been available to our existing customers in the form of the development build.
4) This is not a function which is built into the theme, so it is a modification made by the customer. You can however, find a location related plugin available in the
AppThemes marketplace which allows you to provide a location filter on the homepage. The plugin is called
Multi-City AV. Thanks.