Someone smarter than me can elaborate, but you can set up a PP account to receive only from a buyer's checking account or PP account. The account you have set up does not get charged fees for receiving money. Its called a cash account (tho PP may not call it that). It wont accept money from a debit card. When you pay a seller using your checking account (but not a debit card), or by transferring funds from your own PP account, you are paying with "cash paypal" or "paypal cash".
If you set up an account to receive credit cards or debit cards (in addition to the stuff in the first paragraph), PP will charge you a fee irrespective of where the funds are received from.
I have one of each type. If you buy a light from me and want to send me money straight from your checking account (or straight from your PP acct), I have you send it to my "cash PP" account so I pay no fees. If you want to pay by CC, I have you send it to my "CC PP" account, and I pay a fee to receive your funds.
Hope I'm on track here.
cheers