This is where the law of contracts and customer retention often diverge. You may have a contractual right to sell them 12 baths but if they only want ten and you hold them to the contract, you may find that next time they want to order 50 baths, you don't even get to quote!
A lot of big companies get away with murder on things like this since the small business decides to put up with the breach because they don't want to lose the business altogether. How many other people delivering baths are there in your neck of the woods?