Plaster walls in new construction or use fleece?

And why pay for Q4 when you cover it up afterwards anyway?

What does that have to do with Q4?? We just want to have a 150g painter's fleece glued on it and I wanted to have the surface as smooth as possible. Or rather, it can always happen that the filler sags, if everything is done full-surface, it then sags evenly. At my buddy's place, full-surf.Q4 was sprayed too... looks great. Q4 sprayed 6.5€ per m², sanding extra.

I also don’t see any point in plastering only in Q4 and then putting fleece over it anyway... you achieve the same result already in Q2

Q4 is the highest quality level to achieve an almost perfect visible finish and involves corresponding effort through sanding, which accordingly costs more. If you want to apply fleece anyway, you could have saved yourself the extra cost of Q3 or even Q2.

I was aware that Q4 is the best quality. It was important to me that everything was fully plastered and nice and smooth, our plaster underneath was good, but still somewhat wavy in places when you looked at the wall with grazing light in the evening. Therefore, the painter recommended doing Q4 because he knows me and knew I wouldn’t be happy with Q3 in the end. The total price for the painting was also below the estimated budget, so we are doing the house like this now. I was able to see the result elsewhere and think it will look good.

.man erreicht dasselbe Ergebnis auch in Q2

I don't believe that; although it partly depends on the fleece (thickness, smoothness).