A lot of people dont want to sign up with a website/ do want to use paypal.
Buying on eBay can generally be relatively safe, but you will pay MUCH more than the regular price. As long as you pick a seller that has a good rep and has sold crypos before its ok. if anything goes wrong, paypal almost ALLWAYs sides with the buyer so you can get a charge-back. Selling on the Ebay can be risky. Technically, paypal/ebay don't accept altcoins/cryptos as a product. If you sell, the buyer could issue a charge-back, even though they did receive the coins, so you gotta be careful. if you wanna sell, maybe send them a paper wallet or a usb with the data, so they ave a PHYSICAL object, to avoid gharge-back. Hope I helped with some other questions you may have. Happy crypto-ing!
Edit: Some people can pay more because they know if they issue a charge-back that paypal with give them their $ back. so essentially, they are getting the coins for free.