BuyHub is a search engine for collectors and resellers that covers more than 100 marketplaces worldwide, such as eBay, Vinted, Mercari, Facebook Marketplace, Yahoo Auctions, Kleinanzeigen and Xianyu.

Features:

Search more than 100 marketplaces in 110 countries from a single interface.
Radars that keep searching for you around the clock and notify you the moment a matching item is listed, in your browser and on your phone.
Several search terms across several marketplaces at the same time, with duplicates dropped.
Every result translated into your language, with prices converted to your currency.
Filters the marketplaces do not offer: positive and negative keywords, seller country, listing date.
Saved searches you can open with one click.
Auction alarms that warn you hours or minutes before an auction ends.

BuyHub works on the web, as a browser extension for Chrome and Firefox, and as a mobile app.