why does the client now have to try to find a solution???
Because tone makes the music, which is probably what Hampshire was aiming at.
Unfortunately, in Germany, too often the question of blame is raised instead of constructively looking for a solution.
But if you only focus on the problem, you haven't come a step closer to the solution during that time.
If at the end of the process the only solution is a dismantling including a new installation in order to achieve the originally targeted goal of the walk-in shower, then so be it.
However, one should not exclude everything else from the outset and only see that the contracting party made a mistake.
The craftsman is more likely to be willing to carry it out as agreed if his concerns (especially the enormous effort) have been appropriately acknowledged in a humane way. It then looks like listening to his proposed solutions and discussing whether the suggested approach can correspond to the originally agreed-upon one.