Paypal almost universally sides with the buyer when there's a dispute. It is commonly used by people to run scams.
Order something
pay with paypal
item gets shipped to you
start a dispute with paypal. claim item is wrong, damaged, missing parts, never arrived, etc
paypal takes money back from seller and refunds buyer.
buyer gets to keep the item and their money. seller is screwed.
My other big gripe against paypal is their rules around closing accounts and keeping the money thats in them.
Paypal has a list of items that are legal to buy and sell, but are against their policy. If one of those things is mentioned in a transaction, from either the buyer or seller, paypal's kneejerk reaction is to close both accounts and keep the money in both of them.
Meaning, if I wanted to, I could pick somebody's paypal account from on this board, send them a $5 gift with the word "glock" or "AR-15" in the comments, and laugh as paypal closed their account and kept any money they had in it. The list of no-no words or topics is not listed publicly. There are broad topics that are known. But there is no black and white list. At times, it is completely arbitrary.
If you are selling an item, you can help avoid this my creating the invoice yourself and sending that to the buyer. This prevents them from starting the transaction and having the opportunity to add their own comments. And if you are a buyer, just dont put anything in the comments. You never know what the latest words paypal has in their filter.
Do not keep any balance in your paypal account that you could not afford to lose at any moment. If the account is closed, their policy is keep the money.