Are you using a VPN or a hotspot? The location shown depends on your network settings or your network provider.
If every time you sign in you get a message with a specific location, that may be the location your network is reporting, if the other sign-in details -- time and browser -- correspond to your own sign-in activity.
If you think someone else may be using your credentials to sign in, you should change your eBay password, change email password, and either unlink social media accounts from eBay or change those passwords as well.
