The best way to deal with snakes is to crush their heads/ even with the best of snakes you had better break his neck (lit. crush his head)
Figuratively: do not trust a con artist or swindler of any kind; one should fight him ("ratzutz" means to smash).
("From this they said: ‘The best in Egypt is the slain one, the best among snakes is to crush its head,’ and Pharaoh brought the calamities upon himself and brought Israel to repentance" — Midrash Tanchuma (Warsaw), Beshalach, section 8)
Translation
Expression (Hebrew)
טוֹב שֶׁבַּנְּחָשִׁים רְצֹץ אֶת מוֹחוֹ
Definition (Hebrew)
בְּהַשְׁאָלָה: אֵין לָתֵת אֵמוּן בְּנוֹכֵל אוֹ רַמַּאי מִכָּל סוּג וְיֵשׁ לְהִילָּחֵם בּוֹ (רָצוּץ מַשְׁמָע תְּנַפֵּץ).
("מִכָּאן אָמְרוּ טוֹב שֶׁבְּמִצְרַיִם הָרוּג, טוֹב שֶׁבַּנְּחָשִׁים רְצֹץ אֶת מֹחוֹ, וּפַרְעֹה הִקְרִיב אֶת הַפֻּרְעָנִיּוֹת לָבֹא עָלָיו וְהִקְרִיב אֶת יִשְׂרָאֵל לִתְשׁוּבָה"-מִדְרַשׁ תַּנְחוּמָא (וַרְשָׁא) פָּרָשַׁת בְּשַׁלַּח סִימָן ח)