This is a bit off topic but an issue I see with affirming someone has attained based on asking them to perform fruition repeatedly is that what they are repeating could be a type of wrong release (micchāvimutti) that they are repeating or simply some state that they think is attainment.
The sotapanna has absolutely no doubt that he has attained, he has a profound level of wisdom that has eradicated self view and silabataparamsa (and doubt). The overestimator , or the deluded, may be super confident they too have attained - but this is attachment not wisdom. It gets complicated if they are told by some respected person ‘yes you have attained’, it might increase this wrong perpective.
Thus we rely on the Dhamma: we learn to be independent in the teaching and see what satipatthana really is. Then we won’t - IMHO- look to another to tell us what we know. Of course we do value discussion with the wise, that is one of the ways understanding grows.
Majjhima Nikaya 112 (Bhikkhu Bodhi translation)
Here, bhikkhus, a bhikkhu makes a declaration of final knowledge thus: ‘I understand: Birth is destroyed, the holy life has been lived, what had to be done has been done, there is no more coming to any state of being.’
3. "That bhikkhu’s words should neither be approved nor disapproved. Without approving or disapproving, a question should be put thus: '[..]
" How does the venerable one know, how does he see, regarding these five aggregates affected by clinging, so that through not clinging his mind is liberated from the taints?’
[..]How does the venerable one know, how does he see, regarding these six internal and external bases, so that through not clinging his mind is liberated from the taints?’
So I think it is by questioning and discussion that gradually the wise can be known. But even then we dont have supernormal powers like the ancients who can truly know the mind of others.
Aṅguttara Nikāya 4.192
20. Mahāvagga
Ṭhānasutta
“Bhikkhus, four facts [about people] can be known from four [other] facts. What four?
[…]
“By conversation their wisdom can be known, and this only after a long time, not casually; by one who is attentive, not by one who is inattentive; and by one who is wise, not by one who is unwise..
“Further it was said: ‘By conversation their wisdom can be known, and this only after a long time, not casually; by one who is attentive, not by one who is inattentive; and by one who is wise, not by one who is unwise.’ On account of what was this said?
“Here, bhikkhus, when conversing with someone, one comes to know: ‘Judging from the way this venerable one initiates, formulates, and poses a question, he is unwise, not wise. For what reason? This venerable one does not speak about matters that are deep, peaceful, sublime, beyond the sphere of reasoning, subtle, comprehensible to the wise. When this venerable one speaks on the Dhamma, he is not able to explain, teach, describe, establish, reveal, analyze, and explicate its meaning either briefly or in detail. This venerable one is unwise, not wise.
[[…]
“But in another case, when conversing with someone, one comes to know: ‘Judging from the way this venerable one initiates, formulates, and poses a question, he is wise, not unwise. For what reason? This venerable one speaks about matters that are deep, peaceful, sublime, beyond the sphere of reasoning, subtle, comprehensible to the wise. When this venerable one speaks on the Dhamma, he is able to explain, teach, describe, establish, reveal, analyze, and explicate its meaning both briefly and in detail. This venerable one is wise, not unwise.’ […]: ‘By conversation their wisdom can be known, and this only after a long time, not casually; by one who is attentive, not by one who is inattentive; and by one who is wise, not by one who is unwise.’