Ye Fan believed that with the psychological qualities of the Nine Heavens Mysterious Woman, nothing he could say would likely change her mindset. Instead of testing her, it would be better to be direct and see if she had any "interest" in being honest with him.
He had a plan to confront the Nine Heavens Mysterious Woman directly with force. After all, she claimed to have lost her power and was now just an ordinary mortal, so she shouldn't have the ability to resist his attack. If he did something extreme that she couldn't tolerate, it would reveal whether she truly had cultivation abilities.
But Ye Fan found this approach impractical for the time being because obviously, Sang Yuan became his servant under the Nine Heavens Mysterious Woman's instruction after he helped find her. Acting in such a way would betray trust. The Nine Heavens Mysterious Woman had not overtly done anything to harm Ye Fan, so he couldn't be excessively rude to her, as it might also lose Sang Yuan's trust.
