I first went to Al-Anon in 1994.
Some things I have learned:
If my Higher Power guides me to say 'no', I say 'no'.
I do so kindly, without criticism or attack.
If I explain, I explain briefly.
If the person persists, I just ignore.
I don't argue.
'No' is not the opening salvo of a negotiation.
What they think is none of my business.