Bottom line here is that it's a premium service, and commands a premium price for anything they supply. You're quite within your right to disagree and go about your business. Whether it says fitting is included in the membership is irrelevant, if he had decided to leave it and bought an alternator elsewhere, plus time to fit it DIY or elsewhere he would've saved about £40 if you're lucky. So is the hassle worth it, for me that's a no brainer.