More often than not, a problem isn't down to cached data and clearing it will just mean your system will cache stuff again after.
There are many situations where erasing local cached data and letting the server deliver all new data does fix an issue, though. Typically when a site like eBay changes something about a page that can cause a conflict between the data the site is now actually delivering and the local data stored in the cache from previous visits. When things are working correctly new site data is written seamlessly over the old data and everything displays as it should. When things are not working correctly some users may wind up with a mix of old and new data and some features may stop working until the data no longer conflicts. This overwriting of data can happen on its own over time and may fix the issue entirely, but clearing the cache manually can significantly speed up the process.
Generally if a page or site is not loading correctly, it may be worth trying to refresh the page or use a shift-refresh (a hard refresh which should bypass and overwrite the cached data for the page). Otherwise, if using a different browser allows the page to load correctly, that might be an indication of a problem with the original browser, browser version, cache, cookies, settings or add-ons. Cache and cookies are typically easiest to deal with by clearing the cache and manually erasing the site's cookies, before tackling the relatively harder issues involving problems with settings or add-ons, or updating the browser itself.
Try the easy stuff first before messing with settings and add-ons.
