Srila Prabhupada explains in his purport

A sādhu is not just an ordinary man with a saffron robe or long beard. A sādhu is described in Bhagavad-gītā as one who unflinchingly engages in devotional service. Even though one is found not to be following the strict rules and regulations of devotional service, if one simply has unflinching faith in Kṛṣṇa, the Supreme Person, he is understood to be a sādhu. Sādhurevasamantavyaḥ [Bg. 9.30]. A sādhu is a strict follower of devotional service.

Should one seek material benedictions from such a sadhu?

One should not. Srila Prabhupada adds:

These are the gifts of a sādhu. If we want to associate with a sādhu, we cannot expect him to give us instructions on how to improve our material condition, but he will give us instructions on how to cut the knot of the contamination of material attraction and how to elevate ourselves in devotional service.