A customer bought a self-build greenhouse 7 months ago and emailed last week to say the clips holding the glass to frame are breaking. We have been selling these for nearly 10 years and never had an issue so I suspect a faulty batch during manufacturing. Naturally we have offered to send a new set to replace them. Customer is not happy with this and is asking for compensation (£350 from a £700 purchase price). How should I deal with this? I am certainly not going to give a 50% refund.