Had similar - I argued that my contract to purchase the part was with him, and not his supplier; and he also had a contract with his supplier to send the correct part after he bought it, not me. See the same on eBay when seller posts an item, and in the ad says that if there's an issue with the courier / damaged on arrival etc, then buyer has to take it up with the courier. Nope. buyer has no contract with the courier as I didn't arrange the delivery service...