How are eBay passwords stored in the database? Are the passwords readable by the admins?

All passwords are stored encrypted in the system.
Since encrypted passwords are reversible (otherwise, it would not be able to snipe), developers can read it with some special tools. Although, if you copy the whole database, that will not be enough to decrypt the password. I can even share my encrypted password without any fear of being decrypted.

Also, if you are inactive on the Myibidder for some time, your password will be erased for even higher security of your account.