Welds on the painted railing - assessment?

you are still interpreting the error pattern incorrectly
nothing was welded in picture 2 and 3, so it can't be "weld wire spatter adhesion"

Fortunately, I haven't paid anything yet. Now he has the opportunity to continue looking for a constructive solution with me, which I have offered him. Instead, he insists that his work is completely within the tolerances and threatens with his "dunning department." Unfortunately, holding back 20% on a trade worth 1800 euros doesn’t help me if the railing rusts away in a few years and I have to look at that clumsy touch-up until then.

He also immediately forwarded me the emails in which he was supposed to have arranged an appointment with me. None of them were sent to me or my wife, only to our neighbor and the coordinating construction company. Also, there was no mention of an acceptance; it was only an announcement of when his repair work would take place.
By the way, my neighbors weren’t hit quite as hard because the defects are not as visible but rather on the house-facing edge of the handrail or further down. However, they also are not offered an acceptance appointment.

I’m going to find out now what options I have. So far, I have learned that an expert would cost about 400 euros and that the costs can be reclaimed from the craftsman in case of damage. Can anyone confirm this, and where would you look for such a person? I found a list at the IHK where they are listed by specialization. There is one in the field of welding technology, which I think fits best.

@11ant you are still misinterpreting the fault pattern

That can never be completely ruled out in a remote diagnosis

nothing was welded in picture 2 and 3, so it can't be "weld wire spatter adhesion" either

I also find it baffling how anyone could manage to spray that far – possibly from a workpiece standing next to it in the workshop (?)

Don't you dare. That is not legal.

What is supposed to be illegal about that?
I would name the person if some bungler tries to sell me this nonsense as craftsmanship.
Ant11: The welder did nothing wrong? I took several welding courses at the Chamber of Crafts twenty years ago as part of my training. Although in oxy-fuel welding, but everyone can see that this is shoddy work.

Isn't there something like a right of withdrawal here?
And how exactly did this "acceptance" take place, were you informed about the appointment?

You won't be able to fix all your stinginess damage anyway anymore - except by an absolutely disproportionate and pointless full replacement (at your own expense and no one else's

???
I see it differently. The manufacturer is responsible for damages and also for proper seams. Regardless of what he charges for it.
He can't just say, I'll do it for this and that price but you'll then get a broken railing.

The construction company was able to organize a new acceptance appointment on Friday for us and the neighbors. Let's see if he is more willing to acknowledge his mistakes and offer something reasonably decent when he actually meets his customers in person. I am not optimistic. And the construction company does not give me much hope either and only points out what costs I will face if I go to court and lose. "Railings with much more obvious defects have already been accepted."