Cutting the floor slab due to incorrectly placed drainage pipes

clear, he "must" see that. but something is constantly not seen. most likely not even measured. the client is also somewhat in the "duty" to measure a bit themselves. I also walked through the house with a laser measurer and measured dozens of dimensions with it. it was not about 1-2 cm, but about whether the measurements would probably be correct. everything fit so far

Yes of course, I did that too. I also measured all the penetrations of the base slab, because sometimes it came down to 1-2 cm. We had 13 or 14 pieces, and everything fit perfectly. I am also somewhat preconditioned when it comes to construction. Most homeowners in our circle of acquaintances built according to the approach: "I pay a lot of money for everything, so others should take care of it." The result was sometimes "mediocre."

But I also overlooked things.... you can't be everywhere at once. I just have to live with that now.

incorrectly installed pipes occur more often.

Especially: if at all, then in dozens. The OP's description suggests that it is precisely a reference point that was measured incorrectly, and from which then relatively everything else is actually "correct."

well sure, 1m beside the pipe comes the other pipe and then another 50cm to the next pipe. Great, fits! Pour concrete!

Well, but on the other hand, we also know here the not so uncommon example of first-time builders, who measure with a broken folding rule and desperately proclaim: "Help, [ALL measurements are wrong] !"

So sometimes it just doesn't work. I still remember with us it was like this: you also have a job, and when you were at the construction site in the morning and came back in the evening, suddenly everything was gone. Taking a day off on important days is highly recommended, for example when concrete is being poured or something similar.

But you also need a bit of luck when building a house, otherwise it just goes to sh**.