In this case, I also wouldn’t see why I should pay for the craftsman’s mistakes; as a homeowner, unfortunately, you have to do that way too often because you want to avoid conflict or simply don’t have time. It’s about a lot of money. Every craftsman knows exactly that they have to quote final prices.
I had this trick on a smaller scale once as well. I ordered something from an engraver, 2 engraved signs. Everything discussed, asked for the total price. He said 30€. Okay, seemed cheap to me, but well, they were just small tree signs. When picking them up, they then wanted 2x30€ PLUS VAT.... yeah yeah yeah.... yes, they said they only gave me the net price for one sign. Exactly, because as an end customer, the net price of one sign doesn’t interest me if I’m buying 2 signs. All of a sudden, the 30€ turned into almost 72€. I didn’t pay that either. And I definitely would not pay 6000€ more to the garden landscaper if he gave me his prices wrong beforehand.