יָדַע עַם מִי יֵשׁ לוֹ עֵסֶק

ביטוי (אנגלית)

Know who you're dealing with/ knows exactly who he's dealing with

הגדרה (אנגלית)

To know clearly what kind of person you are dealing with, what to be careful about, and what you can expect from them.

(Modern Hebrew)