What is stopping MasterCard and Visa from banning Coinbase and others if this happens
https://help.coinbase.com/en/coinbase/getting-started/add-a-...
But in the long run you are right: to avoid MasterCard and Visa we should move everything to crypto. It is the only way to control our own destiny.
This is against eBay's policies. All items sold through their site must be delivered physically. If you type "bitcoin" in today you'll only get hardware or novelties, not the coins themselves.
Or do the sale on some other platform that is similar to ebay.