I've been an Ebay seller for 15 years and would never act this way to a customer. Sellers emails and replies are horrible.
It's not that hard to see the buyer made a mistake. Seller should have contacted op and said something like
" Hey I seen you over paid for this part. I'm guessing there was a mistake. here's your $10.00 back."
No, who's wrong or right. No personal bitching or attacking. It's a business, nothing more.
Remind me not to buy from this guy. Ever.