Drainage: Offer €6500, Invoice €8500

Normally, to my knowledge, a supplementary offer must be made.

Normally, to my knowledge, a supplementary offer must be made.

Formally correct, but which trade currently has time for that? The client did not notice that a second inspection shaft was necessary. He would certainly have complained if it had been installed according to the offer and the building authority had demanded the second shaft after months. Just pure speculation that the OP is not responding. I would at least have expected him to write why the second shaft was necessary. As it is, the thread is useless!

Formally correct, but which trade currently has time for that? The client didn’t notice that a second inspection shaft was necessary. He certainly would have complained if it had been installed according to the offer and the building authority had demanded the 2nd shaft after months. It’s pure speculation that the OP isn’t responding. I would have at least expected him to write why the 2nd shaft was necessary. As it is, the thread is useless!

Certainly correct – but at least verbally informing the client about the additional work and extra costs should be possible even for the trade burdened with orders. Communication is the be-all and end-all, I always say.

Life is not a bed of roses

What we perceive as morally right is unfortunately not common practice...

Invoice, raise the price, rest doesn’t matter.

That’s often how it goes, unfortunately.

Life is not a pony farm What we perceive as morally right is unfortunately not common practice ... Issue invoice, raise price, rest doesn't matter. Unfortunately, that's often how it goes.

Sure, as an entrepreneur you can work that way. You just make yourself vulnerable and shouldn't be surprised if the customer then refuses to pay and it ends up causing trouble. No change order offer and no commission usually means a bad starting point for the executing company. Many customers don't care or avoid conflict, meaning in 90 percent of cases it works out well for the executing trade. In the other 10%, the complaining is then loud.

No, there are so-called [sowieso kosten] ... he would have needed it anyway, therefore there is no way to take action against it.