I learned an even better eBay lesson recently...
I bought a set of Raschig pool balls using Buy-It-Now and two hours after my purchase the seller reached out to me and let me know that they had also posted the balls to FB Marketplace and had received a better offer and if I wanted them I would have to pay more money.
I reminded them I had already paid for the balls at the price they had asked for and I was not going to pay more. And by cross-posting the item on other marketplaces they had violated the eBay TOS so I did not care if someone else had offered more.
For the next four hours, they continued to send my messages demanding more money all of which I ignored.
Then eBay let me know that the seller had, and this is the best part... Cancelled the sale at my request.
I then received a new message telling me that they had reposted the balls with a Buy-It-Now $100 more than what I had just paid a couple of hours ago and if I still wanted the balls I could pay the new amount. Which they did as a favor to me...
I told them to choke on a bag of dicks and promptly started fraudulent seller complaints with eBay.
Someone, probably a member of this very forum bought the balls for the new price.
So if you recently bought a set of Raschigs off eBay for $299 bucks, know they are cursed...