Paypal claim, is burden of proof on seller or buyer?

I've been on both ends, got screwed as a buyer, and got screwed as a seller lol. The only thing I know, if you're a buyer you're set. If you've got proof(emails) that you attempted to contact the seller, and never received the item or what not, they'll refund you. I believe they chargeback the seller for it. The only way a seller is covered is if the address the item was shipped to is confirmed through Paypal, & you have an online tracking through the shipping company(delivery confirmation). I didn't use delivery confirmation (my packages are too small for it) the gal claimed she never received it (she did it to a few other people as well). That's when I read through Paypal's policies, and I just went ahead and refunded her rather then deal with the hassle I'd lose anyway. Now, I read on an ebay blog, that delivery confirmation isn't enough as far as paypal is concerned, so I don't know. I've just included shipping insurance on all my stuff, which jacked up my shipping fees real high. Tried contacting paypal through email to ask them that, and they're a joke, I don't think they even bother reading the emails/questions they get. So, long story short lol, to answer your question, the burden is also on the seller.