In those cases (at least when a lot of this was going on with ebay), the trick was that you had to say (or check the box that says) “received incorrect item”. A lot of people, upon buying something for $100 and getting something that costs a dollar are so angry knowing they got scammed, will tell ebay/paypal/their credit card company that they never received the item they ordered. The scammers know you’ll do that. They also know that all they have to is provide the tracking number which proves they sent something to you and that’ll be the end of it.
However, if you say you received the wrong item, now they have to prove that they sent you the correct item.
IIRC from years ago, some ebayers were even running a scam where they could send you the correct item, with proof, and still switch it along the way.