Well, for a start, I wouldn't be dealing with you direct. You'd put your concerns to the customer for them to contact us (with your input if required).
This is a case of a warehouse picking error, not shading like the OP has suggested, so will differ in approach. We have T&C's but we also have sympathy and common sense, so it would go something like this:
I'll say "we", but the supplier acknowledges they have eff'd up and send out the missing tiles immediately (fingers crossed, you are still on the job by the time they arrive).
Its taken you an additional day, to which you put a bill into the customer which they have to pay. Thats you, the fixer, sorted. The customer will then forward us the quote to us, to which the resolution will be negotiated.
So to the problem in hand, she has taken delivery, checked the condition, appears to be in good nick, so signs the paperwork. Fare enough we don't expect it all to be checked on the roadside because thats silly. But they have a delivery note that has the quantities. They don't leave them on the roadside for two weeks until you arrive. So why not when taking them into the house, they count the boxes/tiles? If they got delivered into the house, just double check it. It will also say on the delivery note to check the delivery and notify the supplier if there are any issues within (our case) 48 hours, although we also know this isn't always possible. But really two weeks? And if anyone says after reading this "why should she have to check?", why would anyone have to check a delivery for anything? answer yourself these 3 questions, 1. Is everyone on the planet perfect? 2. Do mistakes happen? 3. Have you never checked a delivery that was in some way incorrect? (lucky bugger if not
)
She's not being asked to do anything difficult, just count and check the condition. And if she did, it would have been spotted, rectified, with 10 days still to spare before you're due to arrive. shouldn't have cost anyone anything, except the supplier for additional carriage of sending the balance.
What would the resolution be? down to the boss, but "my personal hat on" it "should" go 50/50 between the supplier and the customer. With "my company hat on" and being ruled by the manager, customer might get a % refund against their order as goodwill gesture for the inconvenience, which might or might not cover the cost of the additional labour. We have a duty to send the order correct, we failed. The customer has a duty to check the order, they failed. Tiler "we assume" is checking the tiles for quality and shade before fixing. Didn't fit any faulty ones did you? no..... so no liability falls to you.
Again, this is my personal view..... You've done the work. You should be paid, by the customer, with assistance from the supplier. But people shouldn't expect all suppliers to deviate from their T&C's. The
rules of the sale are there in black and white. The customers accepts them on order. But its not the suppliers fault if the customer chooses to ignore them.
I've not read T&C's before and got caught out for a reasonable expense. just had to accept it cuz I couldn't do anything about it. I accepted it at the point I handed the money over. Still don't read them in detail now. Gloss over them maybe. And the chances are I will get caught out again, but ultimately it will be me that has to take responsibility for it.