Sounds like he assumed it would fit his fiesta. His fault clearly, if advertised as an S1 intercooler. If its such a bargain price though, id just refund him, less postage costs, with him paying for return postage. Then bang it up on ebay and no doubt get more for it. Then everyones happy.

You often have to accept that for every 10 good buyers, theres always one that will cause you a bit of hassle. Thats life unfortunatly.