Depending of the amount of money your passing through Paypal, they may request that as a safety measure. I'm buyer and seller, and as a seller, to be able to accept credit card paymenys, i needed a Paypal verified account.
Paypal is safe, you can trust them.
When linked, all your payments will be directly transfered from your bank account by default (there is no need to transfer moyen from your bank account to your paypal balance).
You can change this to pay through your credit card by changing your funds source at each payment.