In a debate, what's it called when you pretend to agree with a point you don't actually agree with, because you think it will make the person more open to agreeing with you on other points?

I'll be honest, if someone was doing that to me, and I figured it out - eventually the contradiction will get teased out as you dig into what they're saying - I would call it "bullshit".

If someone is going to compromise their statements as an attempt to manipulate my state of mind into agreeing with them, then they've shown complete contempt for my ability to understand them by sabotaging my ability to even know what they're saying, and I'd pretty quickly write off any more efforts to understand them. Maybe they've got something worth understanding, but if that's true then presumably someone else more capable and willing to speak their own mind can explain. The first person has proven themselves an unreliable source on anything.

Here's a question for anyone that does this: if you feel the need to lie about your position to make it sound reasonable, what does that say about your position? Maybe it's not actually reasonable? Maybe if you don't believe you can defend your position on its own merits, you don't even really understand it yourself?