Proving Achav Guilty
(ב) וַיְדַבֵּ֣ר אַחְאָ֣ב אֶל־נָב֣וֹת ׀ לֵאמֹר֩ ׀ תְּנָה־לִּ֨י אֶֽת־כַּרְמְךָ֜ וִֽיהִי־לִ֣י לְגַן־יָרָ֗ק כִּ֣י ה֤וּא קָרוֹב֙ אֵ֣צֶל בֵּיתִ֔י וְאֶתְּנָ֤ה לְךָ֙ תַּחְתָּ֔יו כֶּ֖רֶם ט֣וֹב מִמֶּ֑נּוּ אִ֚ם ט֣וֹב בְּעֵינֶ֔יךָ אֶתְּנָה־לְךָ֥ כֶ֖סֶף מְחִ֥יר זֶֽה׃ (ג) וַיֹּ֥אמֶר נָב֖וֹת אֶל־אַחְאָ֑ב חָלִ֤ילָה לִּי֙ מֵֽיהוָ֔ה מִתִּתִּ֛י אֶת־נַחֲלַ֥ת אֲבֹתַ֖י לָֽךְ׃

(2) Ahab said to Naboth, “Give me your vineyard, so that I may have it as a vegetable garden, since it is right next to my palace. I will give you a better vineyard in exchange; or, if you prefer, I will pay you the price in money.” (3) But Naboth replied, “The LORD forbid that I should give up to you what I have inherited from my fathers!”

(ו) וַיְדַבֵּ֣ר אֵלֶ֗יהָ כִּֽי־אֲ֠דַבֵּר אֶל־נָב֨וֹת הַיִּזְרְעֵאלִ֜י וָאֹ֣מַר ל֗וֹ תְּנָה־לִּ֤י אֶֽת־כַּרְמְךָ֙ בְּכֶ֔סֶף א֚וֹ אִם־חָפֵ֣ץ אַתָּ֔ה אֶתְּנָה־לְךָ֥ כֶ֖רֶם תַּחְתָּ֑יו וַיֹּ֕אמֶר לֹֽא־אֶתֵּ֥ן לְךָ֖ אֶת־כַּרְמִֽי׃

(6) So he told her, “I spoke to Naboth the Jezreelite and proposed to him, ‘Sell me your vineyard for money, or if you prefer, I’ll give you another vineyard in exchange’; but he answered, I will not give my vineyard to you.’”

When Navot responded to Achav he said that he wouldn't give up his land because Hashem would be angry he commited a sin. The sin would have been giving up land to another Shevet. However, when Achav told Ezevel what Navot responded, he said Navot wasn't willing to give it up for his own good. Achav didn't mention that Navot wasn't giving up the vineyard for Hashem's sake. By manipulating Navot's response, Achav was delibreailty leading Ezevel down the path to get the vineyard from Navot, since he knew Ezevel's disingenuous ways of getting things done.

(א) שלא לחמד - שלא להעלות במחשבתנו לעשות תחבלה לקחת לנו מה שהוא לזולתנו מאחינו, שנאמר (שמות כ יד) לא תחמד בית רעך וגו'. וכבר הוכיחו ז''ל (מכילתא יתרו) מפסוק אחר דכתיב (דברים ז כה) לא תחמד וגו' ולקחת לך. שאסור לאו דלא תחמד אינו נגמר עד שיעשה בו מעשה. ואפילו נתן הדמים לחבירו על החפץ, עובר גם כן על לאו דלא תחמד, שאין לאו דלא תחמד נתקן בנתינת הדמים כל זמן שדרך הכרח לקחו ממנו, כן הוא הפרוש האמתי לרבותינו ז''ל.

...As once he fixes it into his thought to take the thing that he covets from him, that bad desire will not pay attention to anything; and if his fellow will not want to sell it to him, he will take it from him by force. And if he stands up to him, it is possible that he will [even] kill him; as we found (I Kings 21) that Navot was killed for his vineyard that Ahav coveted from him (See Mishneh Torah, Laws of Robbery and Lost Property 1:11).

Achav was the one that had the bad desire. By bringing on the bad desire to hide wife, he gets blamed for her actions

ואמר רב כל ההולך בעצת אשתו נופל בגיהנם שנאמר (מלכים א כא, כה) רק לא היה כאחאב וגו' א"ל רב פפא לאביי והא אמרי אינשי איתתך גוצא גחין ותלחוש לה לא קשיא הא במילי דעלמא והא במילי דביתא לישנא אחרינא הא במילי דשמיא והא במילי דעלמא

And Rav says: Anyone who follows the counsel of his wife descends into Gehenom, as it is stated: “There was no one like Ahab, who did give himself over to do that which was evil in the sight of the Lord, whom Jezebel his wife incited” (I Kings 21:25). Rav Pappa said to Abaye: But don’t people say a popular proverb: If your wife is short, stoop and whisper to her and consult with her? The Gemara answers: This is not difficult, as this statement of Rav instructs that one not follow her counsel in general matters; and that proverb instructs that one follow her counsel in household matters. The Gemara presents another version of this distinction: This statement of Rav maintains that one should not follow her counsel in divine matters; and that proverb maintains that one should follow her counsel in general matters.

Ezevel is also given blame; but the main blame goes to Achav