I'm not too sure but this is what i found on PayPal:
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Also, I read you can actually check and choose which funding source PayPal will use when you make your payments when both your bank account and credit card are linked to your PayPal account.
When you pay for something, the first thing weâ€™ll do is check your PayPal balance to see if you have enough to cover the payment. If you do, weâ€™ll use your balance to make the payment. If you donâ€™t have money in your balance, you can choose to pay directly from your bank account or your debit or credit card.
To make sure youâ€™re using the payment method you want, click More Funding Options or Change before you send your payment.
* An instant transfer is an immediate transfer from your bank account.
* You must have linked a credit card and bank account to your PayPal account."
Hope this helps. Cheers!
Just remember PayPal is truly safe only when you are using it on eBay. but when you use it off eBay, their primary function is just as a 3rd party payments processor - without the buyer protection program.