Unexpected things happen often - now, just a few years later, I, as the original thread starter, have actually come around to selling a house. Although not my own, I took care of everything.
Due to time constraints, I decided to hire a real estate agent after all - so much for principles. However, to avoid throwing money away for no reason, I set a maximum commission of 3% (that was still last year, when the buyer had to pay the agent in full). The house value was about €350,000 and ~€10,000 seemed more than enough commission.
Things turned out differently and the house was sold to a young family known to me through several connections. So I skipped the agent and did everything myself. I had to realize that it is a bit more work than just taking photos and conducting viewing appointments, but it still never justifies that insane amount (at least for houses that are in normal demand). Even for high earners, the 3% is two full monthly salaries, and although I worked on the sale for a very long time, it was not two months of 40-hour weeks. And this as an amateur.
The end of the story: I would always sell again with an agent but with a max. ~€10,000 commission. The time saved is worth it to me, and the price is justifiable enough that everyone can live with it.
On the other hand: A (good) agent with a 6% commission might have been able to raise the price to €400,000, thus making €50,000 more and taking €24,000 commission. In the end (with the commission split), the seller would still have €38,000 more in their pocket, and that is also a sum not to be underestimated...