I believe that a seller could only accept debit/
credit card payments through gaypal if they had a business account. Not sure about it though.
But I believe a buyer can use their card to pay, either directly, or by creating a gaypal account, adding their card, loading funds, and then paying.
For example, if someone pays with gaypal balance and they get a refund from the seller, the money goes back to their gaypal balance, pretty much instantly. If someone pays with a card through gaypal and a refund is issued, the money goes back to their card (and it takes a little longer for the money to return, it's not instant).
Having said that, someone paying with their card directly has better chances of getting their money back if they have to do a chargeback on the payment. If you pay with gaypal balance and you do a chargeback then you are entirely at gaypal's mercy, and they could easily rule against you, even if you're being totally scammed.
They suck. They suspend accounts for no reason, they freeze your money for 6 months. After 6 months they may even "steal - confiscate" the money if they determine you broke their AUP (Acceptable Use Policy) rules. They can charge you up to $2,500 per violation. I'm serious, it's in their user agreement everyone accepts when registering/using gaypal.
If they suspend you or steal your money, they won't tell you why, they won't tell you what you did wrong or which of their rules you violated, they won't give you a warning or a few days to find a different payment processor. They'll just kick you off and destroy your business and spit in your face. Their customer support is useless too.
Then last I used them, every damn time I tried to login I got hit with a phone verification. And I was using the same browser and everything. It got extremely annoying after a while, especially because I was logging in multiple times per day. And I don't think you can turn off the phone verification. Oh and on occassion I even got hit with a captcha when logging in.
Anyway, there's a million reasons to hate gaypal...
What about their ridiculously high fees and the limits they impose on how you can withdraw/move your money around? There's another one.