They can't "track" you in that sense. As in following you. But they log your IP every time you log into an account. For example:
Account 1:
---------------
123.123.123.1
123.123.123.6
123.123.123.10
Account 2:
---------------
123.123.123.5
123.123.123.9
123.123.123.10
You see? They now know that IP "123.123.123.10" has been used for both Account 1 and Account 2. Now that's usually not enough to suspend an account, because with eBay's millions of users, there will be eventually the same IP's used by 2 accounts on the same day that have nothing to do with each other.
But if you don't clean your cookies or use separate Windows user accounts to keep the cookies separated, they will notice that you're logging into both accounts with the same cookies and there you are....linked!
Do something wrong (or not even) and they will kill both of your accounts.
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