I've had many things go wrong before, after, and during.
We don't have many exclusions. Our warranty is if we made it wrong we fix it within 2 years. It sets us aside from the 1 year companies. As Dave S. mentioned on another recent damage thread, if it makes it thru 2 seasons it should be there forever.
We also do it, because the majority of big jobs are referrals from our long term builders & designers. They tell the clients that we stand by our work.
Our basic exclusion is if the builder, customer, or subcontractor damages it, then we will fix it asap at our hourly rate.
The major exclusion is for what we determine to be risky designs. Wrong wood, finish, or construction. Those instances where the person signing off on it, knows better than us. We push all of the risk onto that person.
Have we negotiated a repair job in the past? Yes, after the job went sideways because they chose to disregard our suggestions. The negotiation is we will fix it our way, not yours.
We have negotiated if its their fault when more work is on the table. If we are half way thru one year's of contracts. We are kinder to the customer. We offer to provide the material at our cost. I may drop the labor rate enough that we are paying our selves, but no extra. I make all of this clear in a damage invoice. If you add all of that up it can save them a fair amount of money. If we don't help financially then we may lose the rest of the work. Also it gives them a reason to bad mouth us to another prospective customer.