I would agree with above about it possibly being a manufacturing fault. However a lot of manufacturers seem to spend more time finding fault with anyone/anything else. I often wonder whether the warranty is worth it as they always seem to blame the installation, sometimes justly sometimes not.
I would definitely try to keep communication open and explain you are in contact with the manufacturer, if it goes further the fact you have endeavoured to resolve goes a long way. My only concern would be as you charged for 'supply and fit' it may be the contract for the customer is with you and not the bath manufacturer, hence your responsibility. While hindsight is a wonderful option, especially with particular customers I would always supply them with a materials list and let them deal with it directly. That way failed deliveries/damage/change of mind etc is not on you.
Just remember it is a business you now run, deal with it in business hours, professionally and try not to let it effect other jobs or out of hours time.
I would definitely try to keep communication open and explain you are in contact with the manufacturer, if it goes further the fact you have endeavoured to resolve goes a long way. My only concern would be as you charged for 'supply and fit' it may be the contract for the customer is with you and not the bath manufacturer, hence your responsibility. While hindsight is a wonderful option, especially with particular customers I would always supply them with a materials list and let them deal with it directly. That way failed deliveries/damage/change of mind etc is not on you.
Just remember it is a business you now run, deal with it in business hours, professionally and try not to let it effect other jobs or out of hours time.