Schopenhauer does not pretend otherwise: the aim is not truth, it is coming out on top in front of an audience. Because he does not pretend, the text works as an inventory. Nearly every manoeuvre he describes can be heard in a project meeting on any given Tuesday.
What I took from it
The move of extending what the other person said. You state something narrow and your counterpart stretches it to an extreme nobody claimed, where it is easy to knock down: "this process can be partly automated" becomes "so you want to replace the accounting team". The response I learned is dull and it works: repeat the exact sentence, without defending the inflated version.
Shifting ground. When the technical argument runs out, the discussion moves to authority, to experience, or to the person. I now name it out loud without hostility, something like that being a different question, and go back to the fact. Naming the swerve defuses it better than answering it.
And the distinction that organises the rest: being right and winning the argument are different outcomes. In a sale, winning the argument and losing the trust is the worst result available, and it is remarkably easy to achieve.
What I left out
All thirty-eight as an operating manual. They work, and using them on someone I am about to spend six months with means winning a Tuesday and losing the project. There is also a genuinely mean streak in the text, particularly where it recommends attacking the person once the arguments run out, which even the author presents as a last resort and which has no elegance whatsoever.