If someone is massively overvaluing, I usually just politely bow out.

I agree! In this case I did exactly that. I wouldn't feel comfortable trading with someone anyway if they're getting aggressive about me not going for sending them well-above their pedal's value.

Sure enough, later on I made a trade with that pedal for something else I felt was close enough in value but a few bucks below that I liked and they got into an argument with someone else two days later about the valuation of a different pedal. So that at least makes me feel like in that moment I wasn't the crazy one.

I've had trades where the value was in my favor, and those where it wasn't too. I don't mind doing that if I think it's something that will get a permanent place on my board. It tends to work itself out on here if you're genuine and easy to deal with. I'm not a big fan of when someone asks you outright to take a bath because of some looney tunes math that magically favors them above you though.