Website limited to certain cities

Hi, I want to launch my web based marketplace with services in few neighboring cities only. So, when a seller tries to sell something from a zip code/city that is not covered, a popup should appear saying that the service is not available and should not allow the seller to add any listing. Similarly, if a buyer tries to search a Zip code/city that is not in the coverage area, a message should be displayed. How can this be achieved?
Note: I am using Woocommerce multi-vendor theme called Makery. Thanks for help!