Try using a different browser as a short term workaround.
If when you check out of eBay and select PayPal, you are sent directly to a specific PayPal account without entering username or password and you do not want that to happen, sign in to that PayPal account outside of eBay if you can and use the Gear icon to go to Settings and choose Security, then check the "Manage your Logins" and "Auto Login" sections and either delete those entries or select "Log out of all devices".
