First of all, while I needed a stool, the store only sold them in pairs (so the cost is 2 x 35 = 70 €). However, I needed it and paid for it, but then I understood why they only sell two together.
Their assembly, while initially seeming like a piece of cake, turns out to be tragically painful. The parts of the stool do not fit as they should, resulting in you trying to screw them together to make them fit. As a result, on one stool, the screw broke, leaving half the piece inside, and it basically gave up. However, I didn't give up; with a special tool that screws in reverse, I removed the piece of the screw, but then I realized that the fittings on the leg of the stool were also damaged. The result ended up in recycling.
In conclusion, people know why they sell them two by two. One is for you to learn, so that you keep the other. Therefore, one stool costs 70 € and not 35 €.
I note that I have purchased many furniture items that require assembly and never had a similar issue with any.
It's simply a very poor construction, and my opinion is to avoid it for something better.
If they were correct, they would refund me the 35 € or the defective stool due to manufacturing. But what am I looking for...