What is the best way to politely tell a potential investor or group of investors that their notion of a fair startup valuation is so insanely greedy that you’d rather jump off a cliff than take that kind of financial haircut?
Just decline politely.
This is what works best.
If they ask why, just say you can’t do the deal at that valuation.
They will either let it drop there. Or they will offer to pay a higher price.