... they could take funds out of my backup bank account which funds my paypal account if I don't have enough in it for purchases? ...

Kat, that's always been the way Ebay operates, surely, when you are buying ? When you complete the buying process, if you don't have sufficient funds in you Paypal account, you are informed that your bank account or credit card will be debited by such and such an amount. They don't do it without your agreement.

Monthly Ebay seller fees will always be deducted from your bank account if you don't have sufficient funds in your Paypal account, but you are always given at least two weeks reminder of what these fees are.