εὐμετάπειστος
From LSJ
ἐξ ὀνύχων λέοντα τεκμαίρεσθαι → judge by the claws, judge by a slight but characteristic mark, small traits give the clue to the character of a person, deduce something from a small indication, identify a lion from its claws
English (LSJ)
A easy to persuade, Arist.EN1151b6, Them.Or.7.98b.