‘No returns’ on the listing
I can write on my lisitng that I am the King of England, doesn’t mean its true or has any validity in law does it.
No returns generally means you cant send it back if you dont like it or bought in error etc.
Sale of Goods doesnt apply to non-business sellers selling second hand goods, but via eBay there is either an express ebay contract for sale (ebay rules) and/or an implied contract for sale.
Simply, you bought Size 8 Men’s shoes, that is clear. They arrived
Size 8 Women’s.
This would appear (regardless of sellers bullish answer) to (in legal parlance) be an innocent misrepresentation. Clear enough because it took STW to point this out to OP himself. You should maintain dignity and point out the unfortunate error to the seller, if that doesnt work stop communicating with him and raise a dispute in ebay that’s what its there for.