Crypto is not good for eBay/Paypal for a couple reasons...
Your considered a money transmitter. In order to legally sell currency, I realize crypto is in kind of a grey area in this regard, IRS considers it a commodity but some government agencies consider it a currency, you need to register with Fincen as an MSB and get Money Transmittr or MSB licenses in any state you sell to. This is incredibly expensive and requires a lot of recordkeeping in terms of compliance. Paypal prohibits MSB's form using their services so if you go about the proper way of selling you are no longer allowed to accept Paypal. Also Paypal and eBay both prohibit currency exchanges from operating using their services so it violates TOS.
Even if crypto wasn't potentially considered a security, your selling a non-tangible good ie your selling something people can hold in their hand. While people do sell gift cards and XBox live cards, they have over the years cracked down on ebooks and other non-tangible items. Even if it was allowed if you sell $100 worth of Crypto, I buy it and you send it to me. All I have to do is say I didn't receive it, they will ask you for a tracking number and without a tracking number you automatically lose the case, I keep your crypto and get my money back. It doesn't matter if you have a blockchain transaction as proof, they aren't gonna look at it.
I see people say "but I see other people selling crypto and even currency on eBay." Alot of people get away with stuff that's against policy, just because someone else is selling it doesn't mean its allowed