It's not about siding with buyer/seller since there are times when they side with seller in few cases such as goods never received and paypal simply said "Contact the seller" and close the dispute.
Well of course they also side with the seller from time to time, depending on the circumstances. But believe me when I say they're
mostly(not 100% of the time) siding with the buyers. I've been an online seller that uses PayPal as my main processor for years and I've had bullshit disputes whereas PayPal sided with the buyer even if it was crystal clear that the buyer was attempting a chargeback scam. Majority of people on eCommerce communities I'm in also hates PayPal with passion because of this reason(especially the ones selling high-ticket items), but they have no choice but to use PayPal as it's one of the most used payment processors.