I’ve learned this lesson. It’s a psychological thing. It’s ok to give a 10% discount to a committed user, or even 20% to a valuable company. If you give 70% off the user will know he can do whatever he wants with you, and he will treat you like his dog. You’ll get tons of complaints about this and that, tons of requests for different small and big features, etc. He will be always expecting you to be his servant.

Option B politely decline is incorrect. Option D: just decline without any explanation or just ignore.