The Torah uses two different words in the tenth commandment. In Exodus it says לֹא תַחְמֹד but in Deuteronomy it adds לֹ֨א תִתְאַוֶּ֜ה. The Rambam qualifies this by saying that one does not transgress לֹא תַחְמֹד until he actually takes the item, either by force or by convincing the person to sell it to him. However, לֹ֨א תִתְאַוֶּ֜ה is transgressed even with thought alone. In either case, one is not liable to a court punishment because it does not count as "an action" that is punishable. (The Raavad disagrees and says the reason he is not liable to punishment is because he can return the item, which takes away the laws punishment).
The Rambam in Gezeila V'aveida 1:9-12
כָּל הַחוֹמֵד עַבְדּוֹ אוֹ אֲמָתוֹ אוֹ בֵּיתוֹ וְכֵלָיו שֶׁל חֲבֵרוֹ אוֹ דָּבָר שֶׁאֶפְשָׁר לוֹ שֶׁיִּקְנֵהוּ מִמֶּנּוּ וְהִכְבִּיר עָלָיו בְּרֵעִים וְהִפְצִיר בּוֹ עַד שֶׁלְּקָחוֹ מִמֶּנּוּ אַף עַל פִּי שֶׁנָּתַן לוֹ דָּמִים רַבִּים הֲרֵי זֶה עוֹבֵר בְּלֹא תַּעֲשֶׂה שֶׁנֶּאֱמַר (שמות כ יד) (דברים ה יח) "לֹא תַחְמֹד". וְאֵין לוֹקִין עַל לָאו זֶה מִפְּנֵי שֶׁאֵין בּוֹ מַעֲשֶׂה. וְאֵינוֹ עוֹבֵר בְּלָאו זֶה עַד שֶׁיִּקַּח הַחֵפֶץ שֶׁחָמַד. כָּעִנְיָן שֶׁנֶּאֱמַר (דברים ז כה) "לֹא תַחְמֹד כֶּסֶף וְזָהָב עֲלֵיהֶם וְלָקַחְתָּ לָךְ". חִמּוּד שֶׁיֵּשׁ בּוֹ מַעֲשֶׂה:
Anyone who covets a servant, a maidservant, a house or utensils that belong to a colleague, or any other article that he can purchase from him and pressures him with friends and requests until he agrees to sell it to him, violates a negative commandment,even though he pays much money for it, as Exodus 20:14 states: "Do not covet."
The violation of this commandment is not punished by lashes, because it does not involve a deed. One does not violate this commandment until one actually takes the article he covets, as reflected by Deuteronomy 7:25: "Do not covet the gold and silver on these statues and take it for yourself." Implied is that the Hebrew tachmod refers to coveting accompanied by a deed
כָּל הַמִּתְאַוֶּה בֵּיתוֹ אוֹ אִשְׁתּוֹ וְכֵלָיו שֶׁל חֲבֵרוֹ. וְכֵן כָּל כַּיּוֹצֵא בָּהֶן מִשְּׁאָר דְּבָרִים שֶׁאֶפְשָׁר לוֹ לִקְנוֹתָן מִמֶּנּוּ. כֵּיוָן שֶׁחָשַׁב בְּלִבּוֹ הֵיאַךְ יִקְנֶה דָּבָר זֶה וְנִפְתָּה בְּלִבּוֹ בַּדָּבָר עָבַר בְּלֹא תַּעֲשֶׂה שֶׁנֶּאֱמַר (דברים ה יח) "לֹא תִתְאַוֶּה" וְאֵין תַּאֲוָה אֶלָּא בַּלֵּב בִּלְבַד
Anyone who desires a home, a wife, utensils, or anything else belonging to a colleague that he can acquire from him, violates a negative commandment at the time he thinks in his heart, "How is it possible to acquire this from him?" and his heart is aroused by the matter, as Deuteronomy 5:18 states: "Do not desire...." Desire refers to feelings in the heart alone
הָא לָמַדְתָּ שֶׁהַמִּתְאַוֶּה עוֹבֵר בְּלָאו אֶחָד וְהַקּוֹנֶה דָּבָר שֶׁהִתְאַוָּה בְּהֶפְצֵר שֶׁהִפְצִיר בַּבְּעָלִים אוֹ בְּבַקָּשָׁה מֵהֶן עוֹבֵר בִּשְׁנֵי לָאוִין. לְכָךְ נֶאֱמַר (שמות כ יד) (דברים ה יח) "לֹא תַחְמֹד" וְ(דברים ה יח) "לֹא תִתְאַוֶּה". וְאִם גָּזַל עָבַר בִּשְׁלֹשָׁה לָאוִין
Thus, we see that a person who desires another person's property violates one negative commandment. One who purchases an object he desires after pressuring the owners and repeatedly asking them, violates two negative commandments. For that reason, the Torah prohibits both desiring and coveting. If he takes the article by robbery, he violates three negative commandments